Method and device for communication between terminals in wireless communication system

ABSTRACT

The present invention relates to a wireless communication system, and more particularly, to a method and device for communication between terminals in a wireless communication system. According to the present invention, a resource configuration method, a channel configuration method, a transmission power control method, etc. for communication between terminals can be provided.

This application is a Continuation of U.S. patent application Ser. No.14/919,348, filed on Oct. 21, 2015, now issued as U.S. Pat. No.9,185,700, which is a Continuation of U.S. patent application Ser. No.13/998,708, filed on Jul. 15, 2013, which is a 35 U.S.C. §371 NationalStage Entry of International Application No. PCT/KR2011/009421 filedDec. 7, 2011 and claims the benefit of U.S. Provisional Application Nos.61/420,322 filed Dec. 7, 2010; 61/427,097 filed Dec. 23, 2010;61/451,077 filed Mar. 9, 2011; 61/475,644 filed Apr. 14, 2011;61/490,601 filed May 27, 2011 and 61/492,354 filed Jun. 1, 2011, all ofwhich are incorporated by reference in their entirety herein.

TECHNICAL FIELD

The present invention relates to a wireless communication system and,more particularly, to a method and device for communication betweenterminals in a wireless communication system.

BACKGROUND ART

FIG. 1 is a diagram showing an example of a wireless communicationsystem to which the present invention is applicable. FIG. 1 shows twokinds of user equipments (UEs): a primary UE directly connected to abase station (e.g., an eNB) 110 to exchange a signal with a network anda secondary UE for exchanging a signal with a network via the primaryUE. FIG. 1 shows a primary UE1 120 and a primary UE2 130 as an exampleof a primary UE and a secondary UE1 140 and a secondary UE2 150 as anexample of a secondary UE. The secondary UE1 140 and the secondary UE2150 may communicate with the primary UE1 120. The primary UE and thesecondary UE may be referred to as a master UE and a slave UE,respectively. For example, the primary UE1 120 may serve to relay asignal transmitted by the secondary UE1 140 and/or a signal transmittedto the secondary UE1 140 between the secondary UE1 140 and the eNB 110.If one UE serves as a relay for another UE, a UE-relay scheme may beapplied. FIG. 1 shows operation for exchanging a signal between theprimary UE1 120 and the secondary UE 140 and/or 150 within coverage ofthe eNB 110.

One or more secondary UEs may be connected to one primary UE and theprimary UE may serve to control transmission/reception operations of aplurality of secondary UEs connected thereto. The primary UE may be, forexample, a general mobile telephone and the secondary UE may be alow-power communication device attached to a laptop computer, a musicplayer or a bio signal sensor. For example, the primary UE and thesecondary UE may be possessed by the same user.

DISCLOSURE Technical Problem

It is necessary to prevent (or minimize) interference from occurring incommunication of other UEs due to communication between a primary UE anda secondary UE. In the example of FIG. 1, communication between anotherUE (e.g., the primary UE2 130) and the eNB 110 has higher priority thancommunication between the primary U1 120 and the secondary UE1 140. Thisis because communication between a UE and an eNB according a previouslydefined scheme is designed without considering communication between aprimary UE and a secondary UE and thus communication between the primaryUE and the secondary UE must be defined so as not to obstructcommunication between the other UE and the eNB. For example,communication between the primary UE1 120 and the secondary UE1 140 ispreferably performed only when there is no real-time trafficcommunication between the primary UE2 130 and the eNB 110.

In addition, communication between the primary UE and the secondary UEneed to avoid interference occurring in communication between other UEs.For example, in a communication environment shown in FIG. 1, assume thatthe primary UE1 120 and the secondary UE1 140 are located close to eachother (e.g., the same user has the primary UE1 120 and the secondary UE1140). Accordingly, the primary UE and the secondary UE may generallyperform communication with low power, because it is possible to reducebattery power consumption of the primary UE and the secondary UE.Meanwhile, the other UE (e.g., the primary UE2 130) and the eNB 110 mayperform communication with relatively high power. Accordingly, sincecommunication between the other UE and the eNB provides stronginterference to communication between the primary UE and the secondaryUE, it is necessary to provide a means for avoiding strong interference.

An object of the present invention devised to solve the problem lies ina method of transmitting/receiving a signal between UEs. Another objectof the present invention devised to solve the problem lies on a resourceconfiguration method, a channel configuration method, a transmit powercontrol method, etc. for communication between UEs. Another object ofthe present invention devised to solve the problem lies in a method forcommunication between UEs and between a UE and a base station in alicensed/unlicensed band.

The technical problems solved by the present invention are not limitedto the above technical problems and other technical problems which arenot described herein will become apparent to those skilled in the artfrom the following description.

Technical Solution

The object of the present invention can be achieved by providing amethod of performing communication between a first user equipment (UE)and a second UE in a wireless communication system including, at thefirst UE, receiving scheduling information including information aboutallocation of resources for communication between the UEs from a basestation, and performing communication between the first UE and thesecond UE based on the scheduling information, wherein a first slot of asubframe among the resources for communication between the UEs includesa control signal for communication between the UEs and a second slot ofthe subframe includes a data signal between the UEs.

In another aspect of the present invention, provided herein is a userequipment (UE) for performing communication between UEs, the UE being afirst UE for performing communication with a second UE in a wirelesscommunication system, including a transmission module for transmitting asignal to an external device, a reception module for receiving a signalfrom an external device, and a processor for controlling the first UE,including the reception module and the transmission module, wherein theprocessor is configured to receive scheduling information includinginformation about allocation of resources for communication between theUEs from a base station and to perform communication with the second UEbased on the scheduling information, wherein a first slot of a subframeamong the resources for communication between UEs includes a controlsignal for communication between the UEs and a second slot of thesubframe includes a data signal between the UEs.

The embodiments of the present invention may include the followingfeatures.

If the resources for communication between the UEs among uplinkresources from the first UE to the base station are allocated, the firstslot may be used to transmit a control signal for the second UE and thesecond slot may be used for transmission/reception between the first andsecond UEs.

If resources for communication between the UEs among downlink resourcesfrom the base station to the first UE are allocated, resources forcommunication between the UEs may be allocated to symbols other than thefirst one or more symbols of the subframe and a control signal for thesecond UE may be additionally transmitted on the second slot.

The first one or more symbols of the subframe may be allocated forcarrier sensing.

A last symbol of the first slot of the subframe may be set to a nullsymbol for transmission-reception switching.

A last symbol of the second slot of the subframe may be set to a nullsymbol for transmission-reception switching or transmit power change.

The scheduling information may be provided to the first and second UEsusing one scheduling message associated with an identifier assigned to apair of the first UE and the second UE.

The scheduling information may be provided to each of the first andsecond UEs using a separate scheduling message associated with anidentifier assigned to each of the first and second UEs.

The second UE may receive a scheduling message associated with anidentifier of the first UE.

The scheduling information may be transmitted from the base station tothe first UE via a random access procedure of the first UE.

The scheduling information may separately include a transmit powercontrol command for transmission from the first UE to the base stationand a transmit power control command for transmission from the first UEto the second UE.

If the second UE reports receive power of a signal from the first UE tothe base station, the transmit power of the signal from the first UE mayhave a fixed value previously specified via high layer signaling or avalue indicated by the base station as an absolute value.

The first UE may periodically or aperiodically report transmit power ofthe signal from the first UE to the base station.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

Advantageous Effects

According to the present invention, it is possible to provide a methodof transmitting/receiving a signal between UEs. In addition, it ispossible to provide a resource configuration method, a channelconfiguration method, a transmit power control method, etc. forcommunication between UEs. In addition, it is possible to provide amethod for communication between UEs and between a UE and a base stationin a licensed/unlicensed band.

The effects of the present invention are not limited to theabove-described effects and other effects which are not described hereinwill become apparent to those skilled in the art from the followingdescription.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a diagram showing an example of a wireless communicationsystem to which the present invention is applicable.

FIG. 2 is a diagram showing the structure of a downlink radio frame.

FIG. 3 is a diagram showing a resource grid of a downlink slot.

FIG. 4 is a diagram showing the structure of a downlink subframe.

FIG. 5 is a diagram showing the structure of an uplink subframe.

FIG. 6 is a diagram showing the configuration of a wirelesscommunication system having multiple antennas.

FIG. 7 is a diagram showing CRS and DRS patterns defined in the existing3GPP LTE system.

FIG. 8 is a diagram showing an uplink subframe structure including anSRS symbol.

FIG. 9 is a diagram showing an example of implementing a transmissionand reception function of an FDD mode relay.

FIG. 10 is a diagram illustrating transmission from a relay to a UE anddownlink transmission from a base station to a relay.

FIG. 11 is a diagram showing the structure of a DL relay subframe.

FIG. 12 is a diagram showing a subframe structure configured in DLresources according to an example of the present invention.

FIG. 13 is a diagram showing a region in which Tx-Rx switching isperformed in a subframe structure according to an example of the presentinvention.

FIG. 14 is a diagram illustrating usage of a last portion of a subframein the subframe structure of FIG. 13 according to an example of thepresent invention.

FIG. 15 is a diagram showing a subframe structure using both first andsecond slots for transmission of a secondary UE according to an exampleof the present invention.

FIG. 16 is a diagram illustrating usage of a last portion of a subframein the subframe structure of FIG. 15 according to an example of thepresent invention.

FIG. 17 is a diagram showing a subframe structure configured in ULresources according to an example of the present invention.

FIG. 18 is a diagram illustrating details of a subframe structureconfigured in UL resources according to an example of the presentinvention.

FIG. 19 is a diagram showing an example of a signal structure used by asecondary UE for random access according to an example of the presentinvention.

FIG. 20 is a diagram showing an exemplary structure of a control channelfor a secondary UE according to an example of the present invention.

FIG. 21 is a diagram showing a wireless communication system in whichcommunication between UEs is performed using resources specified by aneNB according to an example of the present invention.

FIG. 22 is a diagram showing a subframe structure when a primary UEestablishes a separate cell according to an example of the presentinvention.

FIG. 23 is a flowchart of a method for communication between UEsaccording to an embodiment of the present invention.

FIG. 24 is a diagram showing the configuration of atransmission/reception device according to the present invention.

BEST MODE

The following embodiments are proposed by combining constituentcomponents and characteristics of the present invention according to apredetermined format. The individual constituent components orcharacteristics should be considered to be optional factors on thecondition that there is no additional remark. If required, theindividual constituent components or characteristics may not be combinedwith other components or characteristics. Also, some constituentcomponents and/or characteristics may be combined to implement theembodiments of the present invention. The order of operations to bedisclosed in the embodiments of the present invention may be changed toanother. Some components or characteristics of any embodiment may alsobe included in other embodiments, or may be replaced with those of theother embodiments as necessary.

The embodiments of the present invention are disclosed on the basis of adata communication relationship between abuse station and a terminal. Inthis case, the base station is used as a terminal node of a network viawhich the base station can directly communicate with the terminal.Specific operations to be conducted by the base station in the presentinvention may also be conducted by an upper node of the base station asnecessary.

In other words, it will be obvious to those skilled in the art thatvarious operations for enabling the base station to communicate with theterminal in a network composed of several network nodes including thebase station will be conducted by the base station or other networknodes other than the base station. The term “Base Station (BS)” may bereplaced with a fixed station, Node-B, eNode-B (eNB), or an access pointas necessary. The term “relay” may be replaced with a Relay Node (RN) ora Relay Station (RS). The term “terminal” may also be replaced with aUser Equipment (UE), a Mobile Station (MS), a Mobile Subscriber Station(MSS) or a Subscriber Station (SS) as necessary.

It should be noted that specific terms disclosed in the presentinvention are proposed for the convenience of description and betterunderstanding of the present invention, and the use of these specificterms may be changed to another format within the technical scope orspirit of the present invention.

In some instances, well-known structures and devices are omitted inorder to avoid obscuring the concepts of the present invention and theimportant functions of the structures and devices are shown in blockdiagram form. The same reference numbers will be used throughout thedrawings to refer to the same or like parts.

Exemplary embodiments of the present invention are supported by standarddocuments disclosed for at least one of wireless access systemsincluding an Institute of Electrical and Electronics Engineers (IEEE)802 system, a 3^(rd) Generation Project Partnership (3GPP) system, a3GPP Long Term Evolution (LTE) system, and a 3GPP2 system. Inparticular, the steps or parts, which are not described to clearlyreveal the technical idea of the present invention, in the embodimentsof the present invention may be supported by the above documents. Allterminology used herein may be supported by at least one of theabove-mentioned documents.

The following embodiments of the present invention can be applied to avariety of wireless access technologies, for example, CDMA (CodeDivision Multiple Access), FDMA (Frequency Division Multiple Access),TDMA (Time Division Multiple Access), OFDMA (Orthogonal FrequencyDivision Multiple Access), SC-FDMA (Single Carrier Frequency DivisionMultiple Access), and the like. The CDMA may be embodied with radiotechnology such as UTRA (Universal Terrestrial Radio Access) orCDMA2000. The TDMA may be embodied with radio technology such as GSM(Global System for Mobile communications)/GPRS (General Packet RadioService)/EDGE (Enhanced Data Rates for GSM Evolution). The OFDMA may beembodied with radio technology such as Institute of Electrical andElectronics Engineers (IEEE) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE802-20, and E-UTRA (Evolved UTRA). The UTRA is a part of the UMTS(Universal Mobile Telecommunications System). The 3GPP (3rd GenerationPartnership Project) LTE (long term evolution) is a part of the E-UMTS(Evolved UMTS), which uses E-UTRA. The 3GPP LTE employs the OFDMA indownlink and employs the SC-FDMA in uplink. The LTE-Advanced (LTE-A) isan evolved version of the 3GPP LTE, WiMAX can be explained by an IEEE802.16e (WirelessMA-OFDMA Reference System) and an advanced IEEE 802.16m(WirelessMAN-OFDMA Advanced System). For clarity, the followingdescription focuses on the 3GPP LTE and 3GPP LTE-A system. However,technical features of the present invention are not limited thereto.

The structure of a downlink radio frame will be described with referenceto FIG. 2.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) radiopacket communication system, uplink/downlink data packet transmission isperformed in subframe units. One subframe is defined as a predeterminedtime interval including a plurality of OFDM symbols. The 3GPP LTEstandard supports a type 1 radio frame structure applicable to FrequencyDivision Duplex (FDD) and a type 2 radio frame structure applicable toTime Division Duplex (TDD).

FIG. 2(a) is a diagram showing the structure of the type 1 radio frame.A downlink radio frame includes 10 subframes, and one subframe includestwo slots in time domain. A time required for transmitting one subframeis defined in a Transmission Time Interval (TTI). For example, onesubframe may have a length of 1 ms and one slot may have a length of 0.5ms. One slot may include a plurality of OFDM symbols in time domain andinclude a plurality of Resource Blocks (RBs) in frequency domain. Sincethe 3GPP LTE system uses OFDMA in downlink, the OFDM symbol indicatesone symbol duration. The OFDM symbol may be called a SC-FDMA symbol or asymbol duration. A RB is a resource allocation unit and includes aplurality of contiguous subcarriers in one slot.

The number of OFDM symbols included in one slot may be changed accordingto the configuration of a Cyclic Prefix (CP). The CP includes anextended CP and a normal CP. For example, if the OFDM symbols areconfigured by the normal CP, the number of OFDM symbols included in oneslot may be seven. If the OFDM symbols are configured by the extendedCP, the length of one OFDM symbol is increased, and thus the number ofOFDM symbols included in one slot is less than that of the case of thenormal CP. In case of the extended CP, for example, the number of OFDMsymbols included in one slot may be six. If a channel state is instable,for example, if a User Equipment (UE) moves at a high speed, theextended CP may be used in order to further reduce interference betweensymbols.

In case of using the normal CP, since one slot includes seven OFDMsymbols, one subframe includes 14 OFDM symbols. At this time, the firsttwo or three OFDM symbols of each subframe may be allocated to aPhysical Downlink Control Channel (PDCCH) and the remaining OFDM symbolsmay be allocated to a Physical Downlink Shared Channel (PDSCH).

FIG. 2(b) is a diagram showing the structure of the type 2 radio frame.The type 2 radio frame includes two half frames, each of which includesfive subframes, a downlink pilot time slot (DwPTS), a guard period (GP),and an uplink pilot time slot (UpPTS). One of these subframes includestwo slots. The DwPTS is used for initial cell search, synchronizationand channel estimation at a user equipment. The UpPTS is used forchannel estimation of a base station and uplink transmissionsynchronization of the user equipment. The guard period is to removeinterference occurring in an uplink due to multi-path delay of adownlink signal between the uplink and a downlink. Meanwhile, onesubframe includes two slots regardless of a type of the radio frame.

The structure of the radio frame is only exemplary. Accordingly, thenumber of subframes included in the radio frame, the number of slotsincluded in the subframe or the number of symbols included in the slotmay be changed in various manners.

FIG. 3 is a diagram showing a resource grid in a downlink slot. Althoughone downlink slot includes seven OFDM symbols in a time domain and oneRB includes 12 subcarriers in a frequency domain in the figure, thepresent invention is not limited thereto. For example, in case of anormal Cyclic Prefix (CP), one slot includes 7 OFDM symbols. However, incase of an extended CP, one slot includes 6 OFDM symbols. Each elementon the resource grid is referred to as a resource element. One RBincludes 12×7 resource elements. The number N^(DL) of RBs included inthe downlink slot is determined based on a downlink transmissionbandwidth. The structure of the uplink slot may be equal to thestructure of the downlink slot.

FIG. 4 is a diagram showing the structure of a downlink subframe. Amaximum of three OFDM symbols of a front portion of a first slot withinone subframe corresponds to a control region to which a control channelis allocated. The remaining OFDM symbols correspond to a data region towhich a Physical Downlink Shared Channel (PDSCH) is allocated. Examplesof the downlink control channels used in the 3GPP LTE system include,for example, a Physical Control Format Indicator Channel (PCFICH), aPhysical Downlink Control Channel (PDCCH), a Physical Hybrid automaticrepeat request Indicator Channel (MUCH), etc. The PCFICH is transmittedat a first OFDM symbol of a sub-frame, and includes information aboutthe number of OFDM symbols used to transmit the control channel in thesubframe. The PHICH includes a HARQ ACK/NACK signal as a response ofuplink transmission. The control information transmitted through thePDCCH is referred to as Downlink Control Information (DCI). The DCIincludes uplink or downlink scheduling information or an uplink transmitpower control command for a certain UE group. The PDCCH may includeresource allocation and transmission format of a Downlink Shared Channel(DL-SCI), resource allocation information of an Uplink Shared Channel(UL-SCI), paging information of a Paging Channel (PCH), systeminformation on the DL-SCH, resource allocation of an higher layercontrol message such as a Random Access Response (RAR) transmitted onthe PDSCH, a set of transmit power control commands for an individualUEs in a certain UE group, transmit power control information,activation of Voice over IP (VoIP), etc. A plurality of PDCCHs may betransmitted within the control region. The UE may monitor the pluralityof PDCCHs. The PDCCHs are transmitted on an aggregation of one orseveral consecutive control channel elements (CCEs). The CCE is alogical allocation unit used to provide the PDCCHs at a coding ratebased on the state of a radio channel. The CCE corresponds to aplurality of resource element groups. The format of the PDCCH and thenumber of available bits are determined based on a correlation betweenthe number of CCEs and the coding rate provided by the CCEs. The basestation determines a PDCCH format according to a DCI to be transmittedto the UE, and attaches a Cyclic Redundancy Check (CRC) to controlinformation. The CRC is masked with a Radio Network Temporary Identifier(RNTI) according to an owner or usage of the PDCCH. If the PDCCH is fora specific UE, a cell-RNTI (C-RNTI) of the UE may be masked to the CRC.Alternatively, if the PDCCH is for a paging message, a paging indicatoridentifier (P-RNTI) may be masked to the CRC. If the PDCCH is for systeminformation (more specifically, a system information block (SIB)), asystem information identifier and a system information RNTI (SI-RNTI)may be masked to the CRC. To indicate a random access response that is aresponse for transmission of a random access preamble of the UE, arandom access-RNTI (RA-RNTI) may be masked to the CRC.

FIG. 5 is a diagram showing the structure of an uplink frame. The uplinksubframe may be divided into a control region and a data region in afrequency domain. A Physical Uplink Control Channel (PUCCH) includinguplink control information is allocated to the control region. APhysical uplink Shared Channel (PUSCH) including user data is allocatedto the data region. In order to maintain single carrier property, one UEdoes not simultaneously transmit the PUCCH and the PUSCH. The PUCCH forone UE is allocated to a RB pair in a subframe. RBs belonging to the RBpair occupy different subcarriers with respect to two slots. Thus, theRB pair allocated to the PUCCH is “frequency-hopped” at a slot boundary.

Modeling of Multi-Input Multi-Output (MIMO) System

FIG. 6 is a diagram showing the configuration of a wirelesscommunication system having multiple antennas.

As shown in FIG. 6(a), if the number of transmission antennas isincreased to N_(T) and the number of reception antennas is increased toN_(R), a theoretical channel transmission capacity is increased inproportion to the number of antennas, unlike the case where a pluralityof antennas is used in only a transmitter or a receiver. Accordingly, itis possible to improve a transfer rate and to remarkably improvefrequency efficiency. As the channel transmission capacity is increased,the transfer rate may be theoretically increased by a product of amaximum transfer rate R₀ upon using a single antenna and a rate increaseratio R_(i).R _(i)=min(N _(T) ,N _(R))  Equation 1

For example, in an MIMO system using four transmission antennas and fourreception antennas, it is possible to theoretically acquire a transferrate which is four times that of a single antenna system. After theincrease in the theoretical capacity of the MIMO system was proved inthe mid-1990s, various technologies of substantially improving a datatransfer rate have been actively developed up to now. In addition,several technologies are already applied to the various radiocommunication standards such as the third-generation mobilecommunication and the next-generation wireless local area network (LAN).

According to the researches into the MIMO antenna up to now, variousresearches such as researches into information theory related to thecomputation of the communication capacity of a MIMO antenna in variouschannel environments and multiple access environments, researches intothe model and the measurement of the radio channels of the MIMO system,and researches into space-time signal processing technologies ofimproving transmission reliability and transmission rate have beenactively conducted.

The communication method of the MIMO system will be described in moredetail using mathematical modeling. In the above system, it is assumedthat N_(T) transmission antennas and N_(R) reception antennas arepresent.

In transmitted signals, if the N_(T) transmission antennas are present,the number of pieces of maximally transmittable information is N_(T).The transmitted information may be expressed as follows.s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  Equation 2

The transmitted info s₁, s₂, . . . . , s_(N) _(T) may have differenttransmit powers. If the respective transmit powers are P₁, P₂, . . . ,P_(N) _(T) , the transmitted information with adjusted powers may beexpressed as follows.ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T) =[P ₁ s ₁ ,P ₂ s ₂ ,P _(N) _(T) s_(N) _(T) l]^(T)  Equation 3

In addition, ŝ may be expressed using a diagonal a ix P of the transmitpowers as follows.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \mspace{11mu} & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\S_{N_{T}}\end{bmatrix}} = {Ps}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Consider that the N_(T) actually transmitted signals x₁, x₂, . . . ,x_(N) _(T) are configured by applying a weight matrix W to theinformation vector ŝ with the adjusted transmit powers. The weightmatrix W serves to appropriately distribute the transmitted informationto each antenna according to a transport channel state, etc. x₁, x₂ . .. , x_(N) _(T) may be expressed by using the vector X as follows.

$\begin{matrix}{x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 1} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}} = {{W\hat{s}} = {WPs}}}}} & {{Equation}\mspace{14mu} 5}\end{matrix}$

where, w_(ij) denotes a weight between an i-th transmission antenna andj-th information. W is also called a precoding matrix.

In received signals, if the N_(R) reception antennas are present,respective received signals y₁, y₂ . . . , y_(N) _(R) of the antennasare expressed as follows.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  Equation 6

If channels are modeled in the MIMO wireless communication system, thechannels may be distinguished according to transmission/receptionantenna indexes. A channel from the transmission antenna j to thereception antenna i is denoted by h_(ij). In h_(ij), it is noted thatthe indexes of the reception antennas precede the indexes of thetransmission antennas in view of the order of indexes.

FIG. 6(b) is a diagram showing channels from the N_(T) transmissionantennas to the reception antenna i. The channels may be combined andexpressed in the form of a vector and a matrix. In FIG. 6(b), thechannels from the N_(T) transmission antennas to the reception antenna imay be expressed as follows.h _(i) ^(T) =[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  Equation 7

Accordingly, all the channels from the N_(T) transmission antennas tothe N_(R) reception antennas may be expressed as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

An Additive White Gaussian Noise (AWGN) is added to the actual channelsafter a channel matrix H. The AWGN n₁, n₂, . . . , n_(N) _(N) added tothe N_(T) transmission antennas may be expressed as follows.n=[n ₁ ,n ₂ . . . ,n _(N) _(R) ]^(T)  Equation 9

Through the above-described mathematical modeling, the received signalsmay be expressed as follows.

$\begin{matrix}{y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{R}}\end{bmatrix}} + {\quad{\begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix} = {{Hx} + n}}}}}} & {{Equation}\mspace{14mu} 10}\end{matrix}$

The number of rows and columns of the channel matrix H indicating thechannel state is determined by the number of transmission and receptionantennas. The number of rows of the channel matrix H is equal to thenumber N_(R) of reception antennas and the number of columns thereof isequal to the number N_(T) of transmission antennas. That is, the channelmatrix H is an N_(R)×N_(T) matrix.

The rank of the matrix is defined by the smaller of the number of rowsor columns, which is independent from each other. Accordingly, the rankof the matrix is not greater than the number of rows or columns. Therank rank(H) _(of) the channel matrix H is restricted as follows.rank(H)≦min*(N _(T) ,N _(R))  Equation 11

When the matrix is subjected to Eigen value decomposition, the rank maybe defined by the number of Eigen values excluding 0. Similarly, whenthe matrix is subjected to singular value decomposition, the rank may bedefined by the number of singular values excluding 0. Accordingly, thephysical meaning of the rank in the channel matrix may be a maximumnumber of different transmittable information in a given channel.

Reference Signal (RS)

In a wireless communication system, since packets are transmittedthrough a radio channel, a signal may be distorted during transmission.In order to enable a reception side to correctly receive the distortedsignal, distortion of the received signal should be corrected usingchannel information. In order to detect the channel information, amethod of transmitting a signal, of which both the transmission side andthe reception side are aware, and detecting channel information using adistortion degree when the signal is received through a channel ismainly used. The above signal is referred to as a pilot signal or areference signal (RS).

When transmitting and receiving data using multiple antennas, thechannel states between the transmission antennas and the receptionantennas should be detected in order to correctly receive the signal.Accordingly, each transmission antenna has an individual RS.

A downlink RS includes a Common RS (CRS) shared among all UEs in a celland a Dedicated RS (DRS) for only a specific UE. It is possible toprovide information for channel estimation and demodulation using suchRSs.

The reception side (UE) estimates the channel state from the CRS andfeeds an indicator associated with channel quality, such as a ChannelQuality indicator (CQI), a Precoding Matrix Index (PMI) and/or a RankIndicator (RI), back to the transmission side (eNodeB). The CRS may bealso called a cell-specific RS. Alternatively, an RS associated with thefeedback of Channel State Information (CSI) such as CQI/PMI/RI may beseparately defined as a CSI-RS.

The DRS may be transmitted through REs if data demodulation on a PDSCHis necessary. The UE may receive the presence/absence of the DRS from ahigher layer and receive information indicating that the DRS is validonly when the PDSCH is mapped. The DRS may be also called a UE-specificRS or a Demodulation RS (DRS).

FIG. 7 is a diagram showing a pattern of CRSs and DRSs mapped on adownlink RB pair defined in the existing 3GPP LTE system (e.g.,Release-8). The downlink RB as a mapping unit of the RSs may beexpressed in units of one subframe on a time domain×12 subcarriers on afrequency domain. That is, on the time axis, one RB has a length of 14OFDM symbols in case of the normal CP (FIG. 7(a)) and has a length of 12OFDM symbols in case of the extended CP (FIG. 7(b)).

FIG. 7 shows the locations of the RSs on the RB pair in the system inwhich the eNodeB supports four transmission antennas. In FIG. 7,Resource Elements (REs) denoted by “0”, “1”, “2” and “3” indicate thelocations of the CRSs of the antenna port indexes 0, 1, 2 and 3,respectively. In FIG. 7, the RE denoted by “D” indicates the location ofthe DRS.

Hereinafter, the CRS will be described in detail.

The CRS is used to estimate the channel of a physical antenna and isdistributed over the entire band as an RS which is able to be commonlyreceived by all UEs located within a cell. The CRS may be used for CSIacquisition and data demodulation.

The CRS is defined in various formats according to the antennaconfiguration of the transmission side (eNodeB). The 3GPP LTE (e.g.,Release-8) system supports various antenna configurations, and adownlink signal transmission side (eNodeB) has three antennaconfigurations such as a single antenna, two transmission antennas andfour transmission antennas. If the eNodeB performs single-antennatransmission, RSs for a single antenna port are arranged. If the eNodeBperforms two-antenna transmission, RSs for two antenna ports arearranged using a Time Division Multiplexing, (TDM) and/or FrequencyDivision Multiplexing (FDM) scheme. That is, the RSs for the two antennaports are arranged in different time resources and/or differentfrequency resources so as to be distinguished from each other. Inaddition, if the eNodeB performs four-antenna transmission, RSs for fourantenna ports are arranged using the TDM/FDM scheme. The channelinformation estimated by the downlink signal reception side (UE) throughthe CRSs may be used to demodulate data transmitted using a transmissionscheme such as single antenna transmission, transmit diversity,closed-loop spatial multiplexing, open-loop spatial multiplexing, orMulti-User MIMO (MU-MIMO).

If multiple antennas are supported, when RSs are transmitted from acertain antenna port, the RSs are transmitted at the locations of theREs specified according to the RS pattern and any signal is nottransmitted at the locations of the REs specified for another antennaport.

The rule of mapping the CRSs to the RBs is defined by Equation 12.

$\begin{matrix}{{k = {{6m} + {\left( {v + v_{shift}} \right){mod}\; 6}}}{l = \left\{ {{{\begin{matrix}{0,{N_{symb}^{DL} - 3}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots\mspace{14mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{{if}\mspace{14mu} p} - {0\mspace{14mu}{and}\mspace{14mu} l}} \neq 0} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{{if}\mspace{14mu} p} - {1\mspace{14mu}{and}\mspace{14mu} l}} \neq 0} \\{3\left( {n_{s}{mod}\; 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}\;{mod}\; 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}{mod}\; 6}} \right.}}} \right.}} & {{Equation}\mspace{14mu} 12}\end{matrix}$

In Equation 12, k denotes a subcarrier index, 1 denotes a symbol in andp denotes an antenna port index. N_(symb) ^(DL) denotes the number ofOFDM symbols of one downlink slot, N_(RB) ^(DL) denotes the number ofRBs allocated to the downlink, n_(s) denotes a slot index, and N_(ID)^(cell) denotes a cell ID. mod indicates a modulo operation. Thelocation of the RS in the frequency domain depends on a value V_(shift).Since the value V_(shift) depends on the cell ID, the location of the RShas a frequency shift value which varies according to the cell.

More specifically, in order to increase channel estimation performancethrough the CRSs, the locations of the CRSs in the frequency domain maybe shifted so as to be changed according to the cells. For example, ifthe RSs are located at an interval of three subcarriers, the RSs arearranged on 3k-th subcarriers in one cell and arranged on (3k+1)-thsubcarriers in the other cell. In view of one antenna port, the RSs arearranged at an interval of 6 REs (that is, interval of 6 subcarriers) inthe frequency domain and are separated from REs, on which RSs allocatedto another antenna port are arranged, by 3 REs in the frequency domain.

In addition, power boosting is applied to the CRSs. The power boostingindicates that the RSs are transmitted using higher power by bringingthe powers of the REs except for the REs allocated for the RSs among theREs of one OFDM symbol.

In the time domain, the RSs are arranged from a symbol index (I=0) ofeach slot as a starting point at a constant interval. The time intervalis differently defined according to the CP length. The RSs are locatedon symbol indexes 0 and 4 of the slot in case of the normal CP and arelocated on symbol indexes 0 and 3 of the slot in case of the extendedCP. Only RSs for a maximum of two antenna ports are defined in one OFDMsymbol. Accordingly, upon four-transmission antenna transmission, theRSs for the antenna ports 0 and 1 are located on the symbol indexes 0and 4 (the symbol indexes 0 and 3 in case of the extended CP) of theslot and the RSs for the antenna ports 2 and 3 are located on the symbolindex 1 of the slot. The frequency locations of the RSs for the antennaports 2 and 3 in the frequency domain are exchanged with each other in asecond slot.

In order to support spectrum efficiency higher than that of the existing3GPP LTE (e.g., Release-8) system, a system (e.g., an LTE-A system)having the extended antenna configuration may be designed. The extendedantenna configuration may have, for example, eight transmissionantennas. In the system having the extended antenna configuration, UEswhich operate in the existing antenna configuration needs to besupported, that is, backward compatibility needs to be supported.Accordingly, it is necessary to support a RS pattern according to theexisting antenna configuration and to design a new RS pattern for anadditional antenna configuration. If CRSs for the new antenna ports areadded to the system having the existing antenna configuration, RSoverhead is rapidly increased and thus data transfer rate is reduced. Inconsideration of these problems, in an LTE-A (Advanced) system which isan evolution version of the 3GPP LTE system, separate RSs (CSI-RSs) formeasuring the CSI for the new antenna ports may be used.

Hereinafter, the DRS will be described in detail.

The DRS (or UE-specific RS) is used to demodulate data. A precodingweight used for a specific UE upon multi-antenna transmission is alsoused in an RS without change so as to estimate an equivalent channel, inwhich a transfer channel and the precoding weight transmitted from eachtransmission antenna are combined, when the UE receives the RSs.

The existing 3GPP LTE system (e.g., Release-8) supportsfour-transmission antenna transmission as a maximum and the DRS for Rank1 beamforming is defined. The DRS for Rank 1 beamforming is also denotedby the RS for the antenna port index 5. The rule of the DRS mapped onthe RBs is defined by Equations 13 and 14. Equation 13 is for the normalCP and Equation 14 is for the extended CP.

$\begin{matrix}{{k = {{\left( k^{\prime} \right){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix}l} = \left\{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{3N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}{mod}\; 3}}} \right.} \right.} \right.}} & {{Equation}\mspace{14mu} 13} \\{{k = {{\left( k^{\prime} \right){mod}\; N_{sc}^{RB}} + {N_{sc}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \left\{ {{\begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{4N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}{mod}\; 3}}} \right.} \right.} \right.}} & {{Equation}\mspace{14mu} 14}\end{matrix}$

In Equations 13 and 14, k denotes a subcarrier index, 1 denotes a symbolindex, and p denotes an antenna port. N_(SC) ^(RB) denotes the resourceblock size in the frequency domain and is expressed by the number ofsubcarriers. N_(PRB) denotes a physical resource block number. N_(RB)^(PDSCH) denotes the bandwidth of the RB of the PDSCH transmission.n_(s) denotes a slot index, and N_(ID) ^(cell) denotes a cell ID. modindicates a modulo operation. The location of the RS in the frequencydomain depends on a value V_(shift). Since the value V_(shift) dependson the cell ID, the location of the RS has a frequency shift value whichvaries according to the cell.

In the LTE-A system which is the evolution version of the 3GPP LTEsystem, high-order MIMO, multi-cell transmission, evolved MU-MIMO or thelike is considered. In order to support efficient RS management and adeveloped transmission scheme, DRS-based data demodulation isconsidered. That is, separately from the DRS (antenna port index 5) forRank 1 beamforming defined in the existing 3GPP LTE Release-8) system,DRSs for two or more layers may be defined in order to support datatransmission through the added antenna.

Cooperative Multi-Point (CoMP)

According to the improved system performance requirements of the 3GPPLTE-A system, CoMP transmission/reception technology (may be referred toas co-MIMO, collaborative MIMO or network MIMO) is proposed. The CoMPtechnology can increase the performance of the UE located on a cell edgeand increase average sector throughput.

In general, in a multi-cell environment in which a frequency reusefactor is 1, the performance of the UE located on the cell edge andaverage sector throughput may be reduced due to Inter-Cell Interference(ICI). In order to reduce the ICI, in the existing LTE system, a methodof enabling the UE located on the cell edge to have appropriatethroughput and performance using a simple passive method such asFractional Frequency Reuse (FFR) through the UE-specific power controlin the environment restricted by interference is applied. However,rather than decreasing the use of frequency resources per cell, it ispreferable that the ICI is reduced or the UE reuses the ICI as a desiredsignal. In order to accomplish the above object, a CoMP transmissionscheme may be applied.

The CoMP scheme applicable to the downlink may be largely classifiedinto a Joint Processing (JP) scheme and a CoordinatedScheduling/Beamforming (CS/CB) scheme.

In the JP scheme, each point (eNodeB) of a CoMP unit may use data. TheCoMP unit refers to a set of eNodeBs used in the CoMP scheme. The JPscheme may be classified into a joint transmission scheme and a dynamiccell selection scheme.

The joint transmission scheme refers to a scheme for transmitting aPDSCH from a plurality of points (a part or the whole of the CoMP unit).That is, data transmitted to a single UE may be simultaneouslytransmitted from a plurality of transmission points. According to thejoint transmission scheme, it is possible to coherently ornon-coherently improve the quality of the received signals and toactively eliminate interference with another UE.

The dynamic cell selection scheme refers to a scheme for transmitting aPDSCH from one point (of the CoMP unit). That is, data transmitted to asingle UE a specific time is transmitted from one point and the otherpoints in the cooperative unit at that time do not transmit data to theUE. The point for transmitting the data to the UE may be dynamicallyselected.

According to the CS/CB scheme, the CoMP units may cooperatively performbeamforming of data transmission to a single UE. Although only a servingcell transmits the data, user scheduling/beamforming may be determinedby the coordination of the cells of the CoMP unit.

In uplink, coordinated multi-point reception refers to reception of asignal transmitted by coordination of a plurality of geographicallyseparated points. The CoMP scheme applicable to the uplink may beclassified into Joint Reception (JR) and CoordinatedScheduling/Beamforming (CS/CB).

The JR scheme indicates that a plurality of reception points receives asignal transmitted through a PUSCH, the CS/CB scheme indicates that onlyone point receives a PUSCH, and user scheduling/beamforming isdetermined by the coordination of the cells of the CoMP unit.

Sounding RS (SRS)

An SRS is used for enabling an eNodeB to measure channel quality so asto perform frequency-selective scheduling on the uplink and is notassociated with uplink data and/or control information transmission.However, the present invention is not limited thereto and the SRS may beused for improved power control or supporting of various start-upfunctions of UEs which are not recently scheduled. Examples of thestart-up functions may include, for example, initial Modulation andCoding Scheme (MCS), initial power control for data transmission, timingadvance, and frequency-semi-selective scheduling (scheduling forselectively allocating frequency resources in a first slot of a subframeand pseudo-randomly hopping to another frequency in a second slot).

In addition, the SRS may be used for downlink channel qualitymeasurement on the assumption that the radio channel is reciprocalbetween the uplink and downlink. This assumption is particularly validin a Time Division Duplex (TDD) system in which the same frequency bandis shared between the uplink and the downlink and is divided in the timedomain.

The subframe through which the SRS is transmitted by a certain UE withinthe cell is indicated by cell-specific broadcast signaling. 4-bitcell-specific “SrsSubframeConfiguration” parameter indicates 15 possibleconfigurations of the subframe through which the SRS can be transmittedwithin each radio frame. By such configurations, it is possible toprovide adjustment flexibility of SRS overhead according to a networkarrangement scenario. The remaining one (sixteenth) configuration of theparameters indicates the switch-off of the SRS transmission within thecell and is suitable for a serving cell for serving high-rate UEs.

As shown in FIG. 8, the SRS is always transmitted on a last SC-FDMAsymbol of the configured subframe. Accordingly, the SRS and aDemodulation RS (DMRS) are located on different SC-FDMA symbols. PUSCHdata transmission is not allowed on the SC-FDMA symbol specified for SRStransmission and thus sounding overhead does not approximately exceed 7%even when the sounding overhead is highest (that is, even when SRStransmission symbols are present in all subframes).

Each SRS symbol is generated by the basic sequence (random sequence orZadoff-Ch (ZC)-based sequence set) with respect to a given time unit andfrequency hand, and all UEs within the cell use the same basic sequence.At this time, the SRS transmission of the plurality of UEs within thecell in the same time unit and the same frequency band is orthogonallydistinguished by different cyclic shifts of the base sequence allocatedto the plurality of UEs. The SRS sequences of different cells can bedistinguished by allocating different basic sequences to respectivecells, but the orthogonality between the different basic sequences isnot guaranteed.

Relay Node (RN)

A RN may be considered for, for example, enlargement of high data ratecoverage, improvement of group mobility, temporary network deployment,improvement of cell edge throughput and/or provision of network coverageto a new area.

A RN forwards data transmitted or received between the eNodeB and theUE, two different links (backhaul link and access link) are applied tothe respective carrier frequency bands having different attributes. TheeNodeB may include a donor cell. The RN is wirelessly connected to aradio access network through the donor cell.

The backhaul link between the eNodeB and the RN may be represented by abackhaul downlink if downlink frequency bands or downlink subframeresources are used, and may be represented by a backhaul uplink ifuplink frequency bands or uplink subframe resources are used. Here, thefrequency band is resource allocated in a Frequency Division Duplex(FDD) mode and the subframe is resource allocated in a Time DivisionDuplex (TDD) mode. Similarly, the access link between the RN and theUE(s) may be represented by an access downlink if downlink frequencybands or downlink subframe resources are used, and may be represented byan access uplink if uplink frequency bands or uplink subframe resourcesare used.

The eNodeB must have functions such as uplink reception and downlinktransmission and the UE must have functions such as uplink transmissionand downlink reception. The RN must have all functions such as backhauluplink transmission to the eNodeB, access uplink reception from the UE,the backhaul downlink reception from the eNodeB and access downlinktransmission to the UE.

FIG. 9 is a diagram showing an example of implementing transmission andreception functions of a FDD-mode RN. The reception function of the RNwill now be conceptually described. A downlink signal received from theeNodeB is forwarded to a Fast Fourier Transform (FFT) module 912 througha duplexer 911 and is subjected to an OFDMA baseband reception process913. An uplink signal received from the UE is forwarded to a FFT module922 through a duplexer 921 and is subjected to a Discrete FourierTransform-spread-OFDMA (DFT-s-OFDMA) baseband reception process 923. Theprocess of receiving the downlink signal from the eNodeB and the processof receiving the uplink signal from the UE may be simultaneouslyperformed. The transmission function of the RN will now be described.The uplink signal transmitted to the eNodeB is transmitted through aDFT-s-OFDMA baseband transmission process 933, an Inverse EFT (WET)module 932 and a duplexer 931. The downlink signal transmitted to the UEis transmitted through an OFDM baseband transmission process 943, anIFFT module 942 and a duplexer 941. The process of transmitting theuplink signal to the eNodeB and the process of transmitting the downlinksignal to the UE may be simultaneously performed. In addition, theduplexers shown as functioning in one direction may be implemented byone bidirectional duplexer. For example, the duplexer 911 and theduplexer 931 may be implemented by one bidirectional duplexer and theduplexer 921 and the duplexer 941 may be implemented by onebidirectional duplexer. The bidirectional duplexer may branch into theWET module associated with the transmission and reception on a specificcarrier frequency band and the baseband process module line.

In association with the use of the hand (or the spectrum) of the RN, thecase where the backhaul link operates in the same frequency band as theaccess link is referred to as “in-band” and the case where the backhaullink and the access link operate in different frequency bands isreferred to as “out band”. In both the in-band case and the out-bandcase, a UE which operates according to the existing LTE system (e.g.,Release-8), hereinafter, referred to as a legacy UE, must be able to beconnected to the donor cell.

The RN may be classified into a transparent RN or a non-transparent RNdepending on whether or not the UE recognizes the RN. The term“transparent” indicates that the UE cannot recognize whethercommunication with the network is performed through the RN and the term“non-transparent” indicates that the UE recognizes whether communicationwith the network is performed through the RN.

In association with the control of the RN, the RN may be classified intoa RN configured as a part of the donor cell or a RN for controlling thecell.

The RN configured as the part of the donor cell may have a RN ID, butdoes not have its cell identity. When at least a part of Radio ResourceManagement (RRM) of the RN is controlled by the eNodeB to which thedonor cell belongs (even when the remaining parts of the RRM are locatedon the RN), the RN is configured as the part of the donor cell.Preferably, such an RN can support a legacy UE. For example, examples ofsuch an RN include various types of relays such as smart repeaters,decode-and-forward relays, L2 (second layer) relays and Type-2 relays.

In the RN for controlling the cell, the RN controls one or severalcells, unique physical layer cell identities are provided to the cellscontrolled by the RN, and the same RRM mechanism may be used. From theviewpoint of the UE, there is no difference between access to the cellcontrolled by the RN and access to the cell controlled by a generaleNodeB. Preferably, the cell controlled by such an RN may support alegacy UE. For example, examples of such an RN include self-backhaulingrelays, L3 (third layer) relays, Type-1 relays and Type-1a relays.

The Type-1 relay is an in-band relay for controlling a plurality ofcells, which appears to be different from the donor cell, from theviewpoint of the UE. In addition, the plurality of cells has respectivephysical cell IDs (defined in the LTE Release-8) and the RN may transmitits synchronization channel, RSs, etc. In a single-cell operation, theUP may directly receive scheduling information and HARQ feedback fromthe RN and transmit its control channel (Scheduling Request (SR), CQI,ACK/NACK, etc.) to the RN. In addition, a legacy UP (a LE which operatesaccording to the LTE Release-8 system) regards the Type-1 relay as alegacy eNodeB (an eNodeB which operates according to the LTE Release-8system). That is, the Type-1 relay has backward compatibility. The UEswhich operates according to the LTE-A system regard the Type-1 relay asan eNodeB different from the legacy eNodeB, thereby achievingperformance improvement.

The Type-1a relay has the same characteristics as the above-describedType-1 relay except that it operates as an out-band relay. The Type-1arelay may be configured so as to minimize or eliminate an influence ofthe operation thereof on an LI (first layer) operation.

The Type-2 relay is an in-band relay and does not have a separatephysical cell ID. Thus, a new cell is not established. The Type-2 relayis transparent to the legacy UE and the legacy UTE does not recognizethe presence of the Type-2 relay. The Type-2 relay can transmit a PDSCH,but does not transmit at least a CRS and a PDCCH.

In order to enable the RN to operate as the in-band relay, someresources in a time-frequency space must be reserved for the backhaullink so as not to be used for the access link. This is called resourcepartitioning.

The general principle of the resource partitioning in the RN will now bedescribed. The backhaul downlink and the access downlink may bemultiplexed on one carrier frequency using a Time Division Multiplexing(TDM) scheme (that is, only one of the backhaul downlink or the accessdownlink is activated in a specific time). Similarly, the backhauluplink and the access uplink may be multiplexed on one carrier frequencyusing the TDM scheme (that is, only one of the backhaul uplink or theaccess uplink is activated in a specific time).

The multiplexing of the backhaul link using a FDD scheme indicates thatbackhaul downlink transmission is performed in a downlink frequency bandand the backhaul uplink transmission is performed in an uplink frequencyband. The multiplexing of the backhaul link using the TDD schemeindicates that the backhaul downlink transmission is performed in adownlink subframe of the eNodeB and the RN and the backhaul uplinktransmission is performed in an uplink subframe of the eNodeB and theRN.

In the in-band relay, for example, if the backhaul downlink receptionfrom the eNodeB and the access downlink transmission to the UE aresimultaneously performed in a predetermined frequency band, the signaltransmitted from the transmitter of the RN may be received by thereceiver of the RN and thus signal interference or RF jamming may occurin the RF front end of the RN. Similarly, if the access uplink receptionfrom the UE and the backhaul uplink transmission to the eNodeB aresimultaneously performed in a predetermined frequency band, signalinterference may occur in the RF front end of the RN. Accordingly, it isdifficult to implement the simultaneous transmission and reception inone frequency band at the RN unless the received signal and thetransmitted signal are sufficiently separated (for example, unless thetransmission antennas and the reception antennas are sufficientlyseparated from each other (for example, on the ground or under theground) in terms of geographical positions).

As a method for solving the signal interference, the RN operates so asnot to transmit a signal to the UE while a signal is received from thedonor cell. That is, a gap may be generated in the transmission from theRN to the UE and any transmission from the RN to the UE (including thelegacy UE) may not be performed during such a gap. In FIG. 10, a firstsubframe 1010 is a general subframe, in which a downlink (that is,access downlink) control signal and data is transmitted from the RN tothe UE, and a second subframe 1020 is an Multicast Broadcast SingleFrequency Network (MBSFN) subframe, in which a control signal istransmitted from the RN to the UE in a control region 1021 of thedownlink subframe, but any signal is not transmitted from the RN to theUE in the remaining region 1022 of the downlink subframe. Since thelegacy UE expects the transmission of the PDCCH in all downlinksubframes (that is, the RN needs to enable the legacy UEs within its ownarea to receive the PDCCH in every subframe so as to perform ameasurement function), for the correct operation of the legacy UEs, itis necessary to transmit the PDCCH in all the downlink subframes.Accordingly, even on the subframe (the second subframe 1020)) set forthe transmission of the downlink (that is, the backhaul downlink) fromthe eNodeB to the RN, the RN needs to transmit the access downlink infirst N (N=1, 2 or 3) OFDM symbol intervals of the subframe, withoutreceiving the backhaul downlink. Since the PDCCH is transmitted from theRN to the UE in the control region 1021 of the second subframe, it ispossible to provide backward compatibility to the legacy UE served bythe RN. While any signal is not transmitted from the RN to the UE in theremaining region 1022 of the second subframe, the RN may receive thesignal transmitted from the eNodeB. Accordingly, the resourcepartitioning disables the in-band RN to simultaneously perform theaccess downlink transmission and the backhaul downlink reception.

The second subframe 1022 using the MBSFN subframe will now be describedin detail. The MBSFN subframe is for a multimedia broadcast andmulticast service (MBMS) in principle and MBMS means a service forsimultaneously transmitting the same signal by several cells. Thecontrol region 1021 of the second subframe may be a RN non-hearinginterval. The RN non-hearing interval refers to an interval in which theRN does not receive a backhaul downlink signal and transmits an accessdownlink signal. This interval may be set to 1, 2 or 3 OFDM lengths asdescribed above. The RN performs the access downlink transmission to theUE in the RN non-hearing interval 1021 and performs the backhauldownlink reception from the eNodeB in the remaining region 1022. At thistime, since the RN cannot simultaneously perform the transmission andreception in the same frequency band, it takes a certain length of timeto switch the RN from the transmission mode to the reception mode.Accordingly, it is necessary to set a guard time (GT) to switch the RNfrom the transmission mode to the reception mode in a first portion ofthe backhaul downlink reception region 1022. Similarly, even when the RNreceives the backhaul downlink from the eNodeB and transmits the accessdownlink to the UE, a guard time (GT) to switch the RN from thereception mode to the transmission mode may be set. The length of theguard time may be set to values of the time domain, for example, valuesof k (k≧1) time samples Ts or one or more OFDM symbol lengths.Alternatively, if the backhaul downlink subframes of the RN areconsecutively set or according to a predetermined subframe timingalignment relationship, the guard time of a last portion of thesubframes may not be defined or set. Such a guard time may be definedonly in the frequency domain set for the transmission of the backhauldownlink subframe, in order to maintain backward compatibility (thelegacy UE cannot be supported if the guard time is set in the accessdownlink interval). The RN can receive a PDCCH and a PDSCH from theeNodeB in the backhaul downlink reception interval 1022 except for theguard time. Such PDCCH and the PDSCH are physical channels dedicated forRN and thus may be represented by an R-PDCCH (Relay-PDCCH) and anR-PDSCH (Relay-PDSCH).

Communication Between UEs

Communication between a primary UE and a secondary UE proposed by thepresent invention may be performed on uplink (UL) resources or downlink,(DL) resources. If UL resources are used for communication between UEs(a UL frequency band is used in an FDD system and a UL subframe is usedin a TDD system), the UE may fundamentally have transmission capabilityon UL resources in order to transmit a signal to an eNB. In order toapply the present invention, one UE may further have receptioncapability on UL resources in order to communicate with another UE, inaddition to transmission capability on UL resources. Alternatively, ifDL resources are used for communication between UEs (a DL frequency bandis used in an FDD system and a DL subframe is used in a TDD system) theUE may further have transmission capability in addition to receptioncapability on DL resources.

Hereinafter, an embodiment of the present invention in whichcommunication between a primary UE and a secondary UE uses amodification of the existing DL subframe structure will be described. Ifcommunication between UEs is performed using UL resources, a DL subframestructure is used to transmit a signal from one UE to another UE butsuch a DL subframe structure may be used in a band swapping mannerconfigured on UL resources, not on DL resources.

Embodiment 1

The present embodiment relates to a method of using the existing D relaysubframe structure.

FIG. 11 is a diagram showing the structure of the existing DL relaysubframe. The DL relay subframe structure is fundamentally similar tothe second subframe 1020 of FIG. 10 and details thereof will bedescribed with reference to FIG. 11. R-PDCCHs 1120 and 1130 are controlchannels for an RN and may located on OFDM (or SC-FDMA) symbols after aPDCCH 1110 which is a control channel for another macro UE (a UE whichdirectly receives a service from a macro eNB). The RN may transmit aPDCCH to UEs served thereby in a PDCCH region 1110 and then performtransmission-reception (Tx-Rx) switching to receive R-PDCCHs 1120 and1130 from an eNB. In a region in which the RN may receive a signal fromthe eNB, the R-PDCCH 1120 for DL allocation (or DL scheduling) may betransmitted on a first slot and a PDSCH for UL grant (or UL scheduling)or a PDSCH for an RN may be transmitted on a second slot (1130). Afrequency region (e.g., PRBs) in which there is no R-PDCCH transmissionmay be used for PDSCH transmission for the macro UE (1140).

In the present embodiment, the PDCCH region 1110 of FIG. 11 is blank andis used for carrier sensing of the primary UE and/or the secondary UE.FIG. 12 is a diagram showing a subframe structure according to thepresent embodiment.

A UE may sense a carrier signal of a corresponding subframe in a PDCCHregion 1210. Carrier sensing means detecting transmission/reception ofanother adjacent UE in a corresponding region. If it is detected thatanother adjacent UE (e.g., the primary UE 130 of FIG. 1) transmits orreceives a signal in a corresponding subframe, communication between theprimary UE and the secondary UE using relatively low transmit power mayreceive strong interference by signal transmission/reception of anotheradjacent UE. Carrier sensing in the PDCCH region 1210 may be performedby the primary UE and/or the secondary UE. As a result, if it isdetermined that signal transmission/reception of another adjacent UE inthe PDCCH region 1210 of a certain subframe is not performed, thesubframe may be regarded as being used for communication between theprimary UE and the secondary UE.

FIG. 12 shows an example of a subframe structure used for transmissionfrom a primary UE (P-UE) to a secondary UE (S-UE).

If the present embodiment is applied to UL resources, the primary UEwhich was in a transmission mode in a previous subframe additionallyperforms Tx-Rx switching in a part (one or more OFDM (or SC-FDMA)symbols) of a blank region 1210 and then performs carrier sensing in theremaining region until a control channel 1220 for the secondary UE istransmitted. At this time, the control channel for the secondary UE maybe newly defined or the existing channel structure may be reused. Forexample, an R-PDCCH defined in a DL relay subframe structure may be usedas a control channel for S-UE. A control channel transmitted in theexisting data region, such as an R-PDCCH, may be referred to as ane-PDCCH. FIG. 12 shows an example in which the secondary UE operates ina reception mode, in which a second slot 1230 of a PRB in which anR-PDCCH (or an e-PDCCH) is present, may be used to transmit an R-PDCCH(or e-PDCCH) or PDSCH for the secondary UE. A PRB 1240 in which anR-PDCCH is not present may be used to transmit PDSCH for the secondaryUE.

Embodiment 2

The present embodiment relates to a subframe structure when a secondaryLTE operates in a transmission mode. The present embodiment may includea method of utilizing only a second slot and a method of utilizing bothfirst and second slots for transmission of the secondary UE.

Embodiment 2-1

The present embodiment relates to a method of utilizing only a secondslot for transmission of a secondary UE.

FIG. 13 is a diagram showing a region in which Tx-Rx switching isperformed in a subframe structure when only a second slot is utilizedfor transmission of a secondary UE. If only the second slot is utilizedfor transmission of a secondary UE, a primary UE must perform TX-RXswitching in order to receive a signal in a reception mock, A last OFDM(or SC-FDMA) symbol of a first slot as shown in FIG. 13(a) or a firstOFDM (or SC-FDMA) symbol of a second slot as shown in FIG. 13(b) may beused for Tx-Rx switching.

In the subframe structure of the example of FIG. 13, an R-PDCCH (or ane-PDCCH) and PDSCH for the secondary UE may be transmitted on the firstslot. On the second slot, an R-PDCCH (or an e-PDCCH) for the secondaryUE may be transmitted according to circumstances or a PDSCH for theprimary UE or the secondary UE may be transmitted according to atransmission/reception mode of the secondary UE. That is, the PDSCH forthe secondary UE may be transmitted in the reception mode and the PDSCHfor the primary UE may be transmitted in the transmission mode.

The transmission/reception mode of the secondary UE may be determinedvia an indicator included in the R-PDCCH (or the e-PDCCH) of the firstslot. For example, the indicator included in the control channel forS-UE of the first slot may be UL grant for a signal transmitted on thesecond slot. That is, the first slot may be used for DL allocation andUL grant transmission and the second slot may be used for PDSCHtransmission.

Alternatively, the indicator included in the control channel for S-UE ofthe first slot may be defined as a trigger for determining atransmission/reception mode. In this case, a DL relay subframe structuremay be reused in the first slot and UE grant may include an R-PDCCH (oran e-PDCCH) of the second slot. In this case, the secondary UE maypreconfigure a signal to be transmitted based on previously received ULgrant information and transmit the preconfigured signal in an arbitrarysubframe when a trigger indicating transmission is received via acontrol channel for S-UE of a first slot of an arbitrary subframe.

If a signal is transmitted from the primary UE to the secondary UE usingUL resources, the primary UE may not perform Tx-Rx switching betweensubframes when a signal is transmitted to an eNB in a UL subframe nextto a subframe in which transmission to the secondary UE is performed.Accordingly, the primary UE may perform transmission using all OFDM (orSC-FDMA) symbols of the second slot. However, if a difference betweenpower of a signal transmitted to the secondary UE and power of a signalto be transmitted to the eNB in a next subframe is large, a rapid outputpower change is necessary in an amplifier of the primary UE. In order touse a power amplifier for significantly changing an output in a veryshort time, cost may be increased or implementation may be impossible.In this case, a power change interval is necessary in a last portion ofa subframe. Alternatively, if the primary UE transmits a signal to thesecondary UE using DL resources, the primary UE must perform Tx-Rxswitching in order to receive a signal from the eNB in a DL subframenext to a subframe in which transmission to the secondary UE isperformed. Similarly to the primary UE, even in operation of thesecondary UE, a power change interval or a Tx-Rx switching interval maybe necessary in a last portion of one subframe. FIG. 14(a) and FIG.14(b) show examples of defining a Tx-Rx switching interval (or a powerchange interval) in a last portion of a subframe in addition to thesubframe of FIGS. 13(a) and 13(b).

In order to apply the subframe structure shown in FIG. 14, the primaryUE may include an indicator in a control channel for the secondary UE.This indicator may inform the secondary UE as to whether the signaltransmitted by the primary UE also includes a last OFDM (or SC-FDMA)symbol of a corresponding subframe.

Alternatively, the UE may always transmit/receive a signal using OFDM(or SC-FDMA) symbols excluding a last OFDM (or SC-FDMA) symbol withoutdefining a separate indicator. Alternatively, the UE may alwaystransmit/receive a signal using OFDM (or SC-FDMA) symbols including thelast OFDM symbol without defining a separate indicator. In this case, itis possible to simply implement transmission/reception between a P-UEand S-UE without separate control signaling overhead.

Embodiment 2-2

The present embodiment relates to a method of utilizing both first andsecond slots for transmission of a secondary UE.

FIG. 15 shows a subframe structure when both first and second slots areutilized for transmission of the secondary UE. In a method oftransmitting a signal from the secondary UE to the primary UE, as in theexamples of FIGS. 13 and 14, the transmission/reception mode of thesecondary UE in the second slot may not be determined via the R-PDCCH(or the e-PDCCH) in the first slot and the secondary UE may be definedto transmit a signal in both first and second slots at a predefined timeas shown in FIG. 15. In this case, since a Tx-Rx switching interval isnot necessary within a subframe, more OFDM (or SC-FDMA) symbols may beused for signal transmission of the secondary UE. The subframecorresponding to the predefined time when the secondary UE operates inthe transmission mode may be predetermined when a predetermined time haselapsed after UL grant is received (after four subframes (that is, 4ms)). Alternatively, the subframe corresponding to the predefined timewhen the secondary UE operates in the transmission mode may be specifiedvia an R-PDCCH (an e-PDCCH) for the secondary UE and the secondary UEmay perform transmission using both first and second slots in thespecified subframe.

In addition, the secondary UE which receives UL grant may be defined totransmit a signal in one or several subframes after the specified timehas elapsed. In this case, the secondary UE may always performtransmission in only one subframe after the specified time or theprimary UE may indicate the number of subframes used for transmission ofthe secondary UE based on information about a buffer status report ofthe secondary UE when the primary UE transmits UL grant. Alternatively,the number of subframes to be used for transmission may be determined bythe secondary UE. For example, a flag indicating whether continuous datatransmission is performed within a PDSCH for the primary UE may bedefined and the number of subframes to be used for transmission of thesecondary UE may be controlled via this flag information.

Since the primary UE is set to the reception mode at a predefined time,the secondary UE may transmit a signal in all OFDM (or SC-FDMA) symbolsas shown in FIG. 15(a).

Alternatively, as shown in FIG. 15(b), the secondary UE may performcarrier sensing in some OFDM (or SC-FDMA) symbols of a subframe and thentransmit a signal. In this case, if it is determined that the secondaryUE may perform transmission via carrier sensing, the secondary UE maytransmit a signal to the primary UE. If it is determined that signaltransmission may not be performed, the secondary UE may receive new ULgrant and attempt retransmission. Alternatively, subframes forretransmission may be defined in advance and the secondary UE mayattempt retransmission in the subframes and the primary UE, may be setto a reception mode. Alternatively, retransmission may be continuouslyattempted until transmission of the secondary UE becomes possible. Atthis time, the number of subframes which may be used for retransmissionof the secondary UE may be unrestricted or may be restricted to apredetermined value and the primary UE may transmit UL grant if thepredetermined value is reached.

If transmission of the secondary UE on UL resources is performed as inthe example of FIG. 15 and then transmission to the eNB is performed ina next subframe, a power change interval may be necessary.Alternatively, in a next subframe after transmission of the secondary UEon DL resources is performed as in the example of FIG. 15, a Tx-Rxswitching interval may be necessary for DL reception. In this case, asshown in FIG. 16, a Tx-Rx switching interval or a power change intervalmay be defined in a last portion of the subframe.

FIGS. 16(a) and 16(b) show examples of defining a Tx-Rx switchinginterval (or a power change interval) in a last portion of a subframe inaddition to the subframe structure of FIGS. 15(a) and 15(b).

In order to apply the subframe structure shown in FIG. 16, it ispossible to indicate whether a last OFDM (or SC-FDMA) symbol of asubframe is used for transmission of the secondary UE in advance. Forexample, an indicator indicating whether the last OFDM (or SC-FDMA)symbol of the subframe is used for transmission of the secondary UE maybe included in a control channel for the secondary UE. Alternatively,the UE may always use or may not use a last OFDM (or SC-FDMA) symbol ofa subframe without defining a separate indicator. In this case, it ispossible to simply implement transmission/reception between a P-UE andS-UE without separate control signaling overhead.

Embodiment 3

The present embodiment relates to a method of utilizing UL resources (aUL frequency hand in an FDD system and a UL subframe in a TDD system) incommunication between the primary UE and the secondary UE.

According to the present embodiment, since the primary UE already has ULtransmission capability for communication with the eNB, it is possibleto perform communication between the primary UE and the secondary UEwithout additional DL transmission capability. According to the presentembodiment, it is possible to mitigate interference generated bycommunication between another UE and the eNB. For example, since the eNBgenerally transmits a signal with a very high intensity (e.g., a CRS, aprimary synchronization signal (PSS), a secondary synchronization signal(SSS), a physical broadcast channel (PBCH), etc.) using DL resources, ULresources are used for communication between UEs instead of DL resourcesso as to avoid interference generated by a strong signal transmittedfrom the eNB to another UE. If DL resources are used for communicationbetween UEs, communication between the primary UE and the secondary UEmay cause strong UE-to-UE interference when another adjacent UE receivesa DL signal from the eNB. However, in the embodiment, if UL resourcesare used for communication between UEs, interference may not be causedwhen another adjacent UE receives a DL signal from the eNB.

In the present embodiment, a method of utilizing two slots configuringone UL subframe for different purposes is proposed. FIG. 17 is a diagramshowing a UL subframe structure according to the present embodiment. Asshown in FIG. 17, a first slot of one UL subframe may be used for aregion for transmitting/receiving a control signal and a second slotthereof may be used for a region for transmitting/receiving a datasignal. In particular, the second slot used for the data region may beconfigured equally to that used for PUSCH transmission defined in theexisting UE system. For example, configuration of an uplink demodulationreference signal (DMRS), physical resource mapping and modulation andcoding scheme defined in the existing LTE system may be used withoutchange. While PUSCH transmission is performed over two slots of a ULsubframe in the existing UE system, data transmission is performed onlyin the second slot in the present embodiment. In this case, since theexisting PUSCH transmission scheme may be reused for data communicationbetween UEs, it is possible to minimize increase in complexity forimplementing data communication between UEs. In addition, in order tomore simply define communication between UEs, a signal transmitted inthe second slot may be defined to occupy a specific bandwidth inadvance. For example, the signal transmitted in the second slot may bepredefined to occupy an overall system bandwidth.

If UL transmission from the primary UE to the eNB is performed in aspecific UL subframe, the primary UE may not perform communication withthe secondary UE connected thereto in the UL subframe. Accordingly,communication between the primary UE and the secondary UE may berestricted to be performed only in a subframe in which the primary UEdoes not perform transmission to the eNB. The primary UE may be aware ofwhether the primary UE performs UL transmission to the eNB in the ULsubframe in advance. For example, in case of PUSCH, SRS, UL ACK/NACKtransmission dynamically scheduled to the primary UE by the eNB, such ascheduling message may be sent to the UE before a minimum of 4 ms. Inaddition, the eNB may inform the primary UE as to when periodic channelstate information (CSI) report, periodic SRS, semi-persistent schedulingmust be transmitted in advance via higher layer signaling (e.g., RRCsignaling). Accordingly, since the primary UE may determine a subframein which transmission to the eNB is performed in advance, communicationbetween the primary UE and the secondary UE may be performed in theremaining subframes.

Embodiment 4

The present embodiment relates to an OFDM (or SC-FDMA) configurationmethod for carrier sensing among detailed configuration methods of thefirst slot used as a control signal region in a UL subframe.

Referring to FIG. 18, the primary UE and/or the secondary LTE may sensea carrier signal in the first one or plurality of OFDM (or SC-FDMA)symbols 1810 of a subframe. Carrier sensing is used to determine whethertransmission/reception of another adjacent UE is performed. If anadjacent UE performs signal transmission/reception in a subframe,communication between the primary UE and the secondary UE usingrelatively low transmit power may be subject to strong interference. Ifit is determined that signal transmission/reception of another adjacentUE is not performed in a subframe as the result of performing carriersensing by the primary UE and/or the secondary UE, the subframe may beregarded as being used for communication between the primary UE and thesecondary UE.

The size of the region 1810 (that is, the number of OFDM (or SC-FDMA)symbols) in which the primary UE and/or the secondary UE performscarrier sensing may be determined as follows. First, timing advance willbe briefly described. If distances between UEs and an eNB are different,propagation delays from the UEs to the eNB are different. If the eNBreceives uplink subframes from a plurality of UEs, the uplink subframesmay be received at different timings. In order to solve such a problem,the eNB may signal appropriate timing advance values to the UEs, the UEsmay control uplink subframe transmission timings according to thesignaled timing advance values, and, as a result, the eNB may receivethe uplink subframes from the plurality of UEs at the same timing.

If another UE is located far from the primary UE or the secondary UE (onthe assumption that signal transmission/reception of the other UE causesinterference with communication between UEs), a timing advance valueused by the primary UE or the secondary UE and a timing advance valueused by the other UE may be different. In this case, it is necessary tosubstantially consider propagation delay from the other UE to theprimary/secondary UE. That is, a signal transmitted in a first OFDM (orSC-FDMA) symbol of an uplink subframe of the other UE may generateinterference with respect to the primary/secondary UE at timings of theOFDM (or SC-FDMA) symbols other than the first symbol of the uplinksubframe of the primary/secondary UE due to propagation delay.Accordingly, if the number of OFDM (or SC-FDMA) symbols for carriersignal sensing is not sufficient, the signal transmitted by the other UEmay reach the primary/secondary UE after carrier sensing of theprimary/secondary UE has been finished. In order to solve such aproblem, the eNB may set the number of OFDM (or SC-FDMA) symbols 1810 tobe used for carrier sensing by the primary/secondary UE with respect tothe primary/secondary UE via a higher layer signal, etc. For example,the eNB may inform the primary/secondary UE of the number of OFDM (orSC-FDMA) symbols 1810 to be used for carrier sensing based on a distanceof the other UE which may obstruct communication between the primary UEand the secondary UE within the cell.

The transmission/reception operation of the primary UE and/or thesecondary UE may be determined according to the carrier sensing result.For example, the primary UE may schedule and transmit data transmissionin the second slot to the secondary UE if another adjacent UE is notdetected as the carrier sensing result. Similarly to the primary UE, thesecondary UE may perform carrier sensing before a transmission operationand perform a transmission operation in the second slot according to aninstruction of the primary UE only when another UE which performscommunication in the subframe is not detected.

Embodiment 5

The present embodiment relates to a method of configuring a controlchannel for a secondary UE among detailed configuration methods of afirst slot used as a control signal region in a UL subframe. That is,the primary UE may transmit a control channel for the secondary UE (on1820 of FIG. 18) using some OFDM (or SC-FDMA) symbol(s) after an OFDM(or SC-FDMA) symbol in which carrier sensing is performed. An indicator(Tx/Rx indicator) indicating whether the secondary UE performs atransmission operation or a reception operation in the second slot ofthe subframe may be included in the control channel for the secondary UEof the first slot.

If the indicator (Tx/Rx indicator) included in the control channel forthe secondary UE indicates transmission of the secondary UE in a certainsubframe, the primary UE may add an identifier of the secondary UE tothe control channel. Thus, the secondary UE having the identifier may beinstructed to transmit data in the second slot of the subframe.

In addition, the secondary UE which receives the identifier maymultiplex an ACK/NACK signal indicating whether data received from theprimary UE is successfully received (or decoding is successfullyperformed) with data (1840 of FIG. 18) transmitted in the second slotand transmit the multiplexed signal. The operation of multiplexing theACK/NACK signal with the data by the secondary UE may be performedaccording to an instruction of the primary UE and the primary UE may addan ACK/NACK multiplexing request indicator to the control channel forthe secondary UE.

In this case, as an example of multiplexing the ACK/NACK signal with thedata by the secondary UE, a method of piggybacking a PUCCH on a PUSCHmay be used. As such a piggybacking method, as defined in 3GPP LTE, ifPUCCH transmission and PUSCH transmission must be simultaneouslyperformed, a method of piggybacking the PUCCH on resources allocated forthe PUSCH may be reused. That is, the secondary UE may insert theACK/NACK signal into a portion of resources (1840 of FIG. 18) used totransmit data instead of the data signal transmitted by the secondary UEand transmit the resources to the primary UE.

If ACK/NACK indicating, whether one or more pieces of data have beensuccessfully received from the primary UE up to now must be transmitted,ACK information is transmitted only when all one or more pieces of datahave been successfully decoded and, otherwise (that is, if one or morepieces of data fails to be decoded) NACK information is transmitted.

If the primary UE transmits the control channel indicating that thesecondary UE will receive data to the secondary UE but the secondary UEdoes not detect the control channel, the secondary UE does not receivedata indicated by the control channel which is not detected. However,since the secondary UE is not aware that the primary UE has transmittedthe control channel and the data, the secondary UE may determine thatall data transmitted by the primary UE has been received and transmitACK, although specific data fails to be received. ACK transmitted fromthe secondary UE to the primary UE may not indicate reception failure.In order to prevent such a problem, the primary UE may use a counterindicating the number of times of transmission of data to a specificsecondary UE. That is, the primary UE may increase the counter one byone whenever data is transmitted to the secondary UE and check whetherthe secondary UE does not receive specific data of a plurality of piecesof data.

If the indicator (Tx/Rx indicator) included in the control channel forthe secondary UE indicates transmission of the secondary UE in a certainsubframe but does not include the identifier of a specific secondary UE,the primary UE may use the second slot of the subframe for random accessof the secondary UEs. Alternatively, the second slot may be indicatedfor random access of the secondary UEs using a predefined specialindicator (alternatively, the above Tx/Rx indicator may have apredefined special value) included in the control channel for thesecondary UE. That is, if the secondary UE, receives the indicatorindicating transmission but the indicator does not include theidentifier of the specific UE or if the predefined special indicator isincluded, the secondary UE may perform a random access procedure.Through the random access procedure, the secondary UE may transmit, tothe primary UE, a signal (scheduling request) for requesting schedulingof the secondary UE or a signal (buffer status report) indicatinginformation such as the amount of data stored in a buffer thereof.

FIG. 19 is a diagram showing an example of a signal structure used by asecondary UE for random access. The example of the signal used forrandom access of FIG. 19 may be transmitted from the secondary UE to theprimary UE in the data region 1840 of the second slot of FIG. 18. In theexample of FIG. 19, the secondary UE transmits a preamble for signaldetection or channel estimation and then transmits payload such assecondary UE ID, scheduling request or buffer status report. Here, sincecommunication between UEs is performed over a short distance, thepreamble preferably occupies a small number of SC-FDMA symbols ifpossible. For example, random access preamble format 4 defined in 3GPPLTE may be reused as the preamble (see section 5.7.1 of 3GPP TS 36.211).In addition, in order to enable the primary UE to more easily detectrandom access from the secondary UE, resources (RBs) used for randomaccess from the secondary UE may be predefined or restricted toresources specified by the primary UE.

If the indicator (Tx/Rx indicator) included in the control channel forthe secondary UE indicates reception of the secondary UE in a certainsubframe, the primary UE may add the secondary UE ID to the controlchannel and indicate that the secondary having the identifier receivesdata in the second slot of the subframe. Alternatively, if the indicator(Tx/Rx indicator) included in the control channel for the secondary UEindicates reception of the secondary UE in a certain subframe, theprimary UE may include a predefined specific indicator in the controlchannel and indicate that all secondary UEs connected to the primary UEreceive data in the second slot of the subframe. This is advantageouswhen a variety of control information which must be received by allsecondary UEs is transmitted via the data region (1840 of FIG. 18).

Additionally, the control channel for the secondary UE in a certainsubframe may include a variety of control information such as anACK/NACK signal indicating whether the primary UE successfully receivesdata previously transmitted by the secondary UE. The structure of such acontrol channel will be described with reference to FIG. 20.

FIG. 20 is a diagram showing an exemplary structure of a control channelfor a secondary UE. The control channel shown in FIG. 20 may betransmitted from the primary UE to the secondary UE on the controlchannel region 1820 of the first slot of FIG. 18. As shown in FIG. 20,the control channel may include a preamble and a payload thatrespectively correspond to the preamble 1821 and the control channelpayload 1822 of FIG. 18. The preamble of the control channel may be usedfor signal detection and channel estimation and the payload of thecontrol channel may include a Tx/Rx indicator indicatingtransmission/reception of the secondary UE, a secondary UE ACK/NACK,etc.

The random access format of the secondary UE shown in FIG. 19 and thebasic structure of the control channel for the secondary UE shown inFIG. 20 are equally designed to further reduce complexity of the UEoperation.

As shown in FIG. 18, the last one or plurality of OFDM (or SC-FDMA)symbols 1830 of the first slot may be set to null symbol(s) in which nosignal is transmitted by the primary UE. During this portion 1830, Tx-Rxswitching of the primary UE and/or the secondary UE may be performed.Next, a configuration method of a second slot of a subframe structureproposed by the present invention will be described.

Embodiment 6

The present embodiment relates to a detailed configuration method of asecond slot used as a data signal region in a UL subframe.

If the primary UE must receive a signal from the secondary UE in acertain subframe and transmit a signal to the eNB in a next subframe, inorder to ensure a time for switching the primary UE from a receptionmode to a transmission mode, last one (or a plurality of) OFDM (orSC-FDMA) symbols of the subframe may not be used for signal transmissionof the secondary UE (signal reception by the primary UE from thesecondary UE). That is, a Tx-Rx switching region 1850 of FIG. 18 may beconfigured. The primary UE may include an indicator indicating whetherthe last one or plurality of OFDM (or SC-FDMA) symbols of the secondslot is used for data transmission in the control channel 1820 for thesecondary UE of the first slot. Alternatively, the secondary UE whichreceives information indicating transmission to the primary UE in thesecond slot may always perform data transmission using only the OFDM (orSC-FDMA) symbol of the second slot excluding the last one (or theplurality of) OFDM (or SC-FDMA) symbols. In this case, an indicatorindicating whether the last OFDM (or SC-FDMA) symbol of the second slotis used does not need to be included in the control channel of the firstslot such that the UE operation is more simply defined.

Meanwhile, if the primary UE must transmit a signal to the second UE ina certain subframe and transmit a signal to the eNB in a next subframe,Tx/Rx switching of the primary UE is not necessary. Accordingly, theprimary UE may use all OFDM (or SC-FDMA) symbols of the second slot fordata transmission. If a difference between power of a signal transmittedfrom the primary UE to the secondary UE in the subframe and power of asignal transmitted to the eNB in a next subframe is large, power outputfrom the amplifier of the primary UE is rapidly changed. Thus, it isnecessary to configure a power change interval similarly to theabove-described Tx-Rx switching interval 1850.

The primary UE may include one indicator in the control channel for thesecondary UE and inform the secondary UE as to whether the datatransmitted by the primary UE is included even in the last OFDM (orSC-FDMA) symbol or whether the power change interval is configured usingthis indicator. Alternatively, without defining this indicator, theprimary UE may be configured to always transmit data using symbolsexcluding the last OFDM (or SC-FDMA) symbols. In this case, it ispossible to mitigate complexity of the UE operation.

Embodiment 7

Scheduling of signal transmission/reception to/from the secondary UE bythe primary UE was described in the above-described examples.Hereinafter, as another method for communication between UEs proposed bythe present invention, a method of directly scheduling communicationbetween UEs at an eNB will be described. However, examples of subframestructures, resource configurations and channel structures described inEmbodiments 1 to 6 or one or more combinations thereof are applicable tothe method of directly scheduling communication between UEs at the eNB.

If the eNB directly performs scheduling of communication between UEs,the primary UE and the secondary UE read a scheduling message of the eNB(e.g., a UL/DL scheduling message transmitted by the eNB via a PDCCH)and confirm on which resource communication between UEs is scheduled orwhen communication between UEs is scheduled.

Embodiment 7-1

The present embodiment relates to a method of reading the samescheduling message at a primary UE and a secondary UE.

The eNB may transmit one scheduling message and two UEs (the primary UEand the secondary UE) read this message and confirm information aboutcommunication between UEs. The eNB may configure a UE communication pairfor performing mutual communication. One UE communication pair mayinclude one primary UE and one secondary UE in case of unicast orinclude one primary UE and a plurality of secondary UEs in case ofmulticast. From the viewpoint of the eNB, a plurality of UEcommunication pairs may be configured. The eNB may assign a uniqueidentifier (ID) to each UE communication pair and transmit a schedulingmessage according to the ID of the UE communication pair. The UEbelonging to each UE communication pair may detect a scheduling messageusing the ID assigned to the UE communication pair to which the UEbelongs (for examples, decodes a PDCCH CRC-masked with the UEcommunication pair ID), thereby confirming scheduling information(resources such as time/frequency) of the UE communication network pairto which the UE belongs.

The UE communication pairs may be assigned separate IDs according todirectivity. For example, assume that transmission/reception between twoUEs (e.g., UE1 and UE2) is alternately and repeatedly performed. In thiscase, the eNB may assign one ID to a UE communication pair which istransmitted by the UE1 and received by the UE2 and assign another ID toa UE communication pair which is transmitted by the UE2 and received bythe UE1. If the ID is assigned to the UE communication network pairaccording to the transmission/reception direction, since a determinationas to which UE performs transmission or which UE performs reception ismade by only decoding the scheduling message (that is, since a separatesignal indicating a transmission UE or a reception UE is not necessary),it is possible to reduce complexity of the UE operation.

However, if the ID assigned to the UE communication pair variesaccording to directivity, the number of IDs to be assigned to individualUEs by the eNB may be increased as compared to the case in which the IDis assigned to the UE communication pair regardless of directivity (thatis, without distinction between the transmission/reception side).Accordingly, the ID may be assigned to the UE communication pairregardless of directivity without distinction between thetransmission/reception side (that is, the same ID is assigned to the UEcommunication pair which is transmitted by the UE1 and received by theUE2 and the UE communication pair which is transmitted by the UE2 andreceived by the UE1). In this case, a separate signaling field may bedefined in a scheduling message to indicate a transmission side and areception side.

If the ID is assigned to the UE communication pair, one UE may have twoor more IDs with respect to UL transmission. For example, one ID is forUL transmission to the eNB and another ID is for transmission to anotherUE.

A variety of uplink control information indicated by the eNB may beseparately managed according to ID. For example, in case of closed looppower control for increasing or decreasing transmit power during acertain time to a predetermined level as compared to the existingtransmit power, the UE may accumulate only power control commandtransmitted via the same ID and accumulate power control commandstransmitted via another ID. This is because the reception side to bescheduled is changed according to ID and thus the appropriate powercontrol value is changed according to the reception side. For example,if the eNB does not indicate what receives uplink control information(e.g., an eNB or a UE), the UE which receives uplink control informationis not directly aware of an uplink transmission destination but appliescontrol information of uplink transmission which varies according todestinations if uplink control information is managed using the IDassigned according to the uplink reception side.

Alternatively, in case of transmission for communication between UEs,transmit power having a predetermined level (e.g., minimum transmitpower) may be defined in advance without separate power control. Sincecommunication between UEs is generally performed over a short distance,communication may be performed with low transmit power. In this case, beeNB may not provide an uplink power control command to a UEcommunication pair ID for communication between UEs or the UE may ignorethe power control command if the power control command is included inthe scheduling message for the UE communication pair ID.

Embodiment 7-2

The present embodiment relates to a method of reading a separatescheduling message at a primary UE and a secondary UE.

The eNB may transmit a separate scheduling message to UEs thatcommunicate with each other. Each UE may read the scheduling messagecorresponding to the ID thereof and detect the location of resourcesused to schedule communication between the UEs. In this method, sincethe ID used for communication between each UE and the eNB may be used ina scheduling message for communication between UEs, it is possible tomitigate complexity of the UE operation in view of detection of thescheduling message. For example, since the UE performs PDCCH blinddecoding with only one ID regardless of whether communication with theeNB or communication with another DE is performed, PDCCH blind decodingis not performed with an ID which varies according to the type of acommunication counterpart and thus decoding delay may be reduced.

If only one ID is assigned to each UE regardless of the type of thecommunication counterpart, the eNB may define a separate signaling fieldin the scheduling message and indicate whether scheduling information isfor transmission to the eNB or transmission to another UE or whether theUE which receives the scheduling message receives a signal from anotherUE using the field.

In addition, the signaling field (the field indicating the communicationcounterpart and the transmission/reception side) may be associated withuplink power control of the which receives the scheduling message. Thatis, the power control command is transmitted via a PDCCH masked with thesame ID regardless of the communication counterpart, but the powercontrol command must be separately accumulated if the content of thesignaling field is the same. For example, the power control commandincluded in the scheduling message must be added to the power controlcommands included in the scheduling message for transmission to the eNBif the scheduling message received at a specific time is fortransmission to the eNB and must not be added to the power controlcommands included in the scheduling message in the other case (e.g.,transmission to another UE).

Alternatively, in case of transmission for communication between UEs,transmit power having a predetermined level (e.g., minimum transmitpower) may be defined in advance without separate power control. Sincecommunication between UEs is generally performed over a short distance,communication may be performed with low transmit power. In this case,the eNB may not include an uplink power control command in thescheduling message for communication between UEs or the UE may ignorethe power control command if the power control command is included inthe scheduling message.

Embodiment 7-3

The present embodiment relates to a method of reading a schedulingmessage of a primary UE at a secondary UE.

According to the present embodiment, the primary UE may operate equallyto Embodiment 7-2. That is, the primary UE may reuse the ID used forcommunication with the eNB without change and receive a schedulingmessage for communication between UEs. In this case, the eNB may notassign a separate ID to the secondary UE.

Meanwhile, the secondary UE may receive the ID of the primary UE fromthe eNB via a higher layer signal in advance and attempt to detect thescheduling message with the ID of the primary UE. This may mean that thesecondary UE overhears the scheduling message from the eNB to theprimary UE. If the scheduling message is successfully read, thesecondary UE may check when the primary UE transmits a signal theretousing which resources.

It is necessary to determine whether the scheduling message for theprimary UE read by the secondary UE is for transmission from the primaryUE to the eNB or for transmission from the primary UE to the secondaryUE. Accordingly, an indication field indicating a transmissiondestination of the primary UE may be added to the scheduling message.

The present embodiment is particularly advantageous in that a simpleoperation is possible without burden on blind decoding of the schedulingmessage if the secondary UE is not directly connected to the eNB andthus the secondary UE is not assigned an ID to be used to directlytransmit a signal to the eNB.

Embodiment 7-4

The present embodiment relates to a method of reading a schedulingmessage using a random access procedure.

The primary UE may transmit a physical random access channel (PRACH)preamble to the eNB to request allocation of resources for communicationbetween UEs. At this time, a PRACH preamble index, location of time andfrequency resources, etc. for requesting communication between UEs maybe predefined via a higher layer signal with respect to an individualprimary UE. The primary UE which requires communication between UEs maytransmit a PRACH preamble using predefined resources and attempt todecode a PDCCH masked with an RA-RNTI during a predetermined time. TheRA-RATI is determined by the location of resources used to transmit thePRACH. As described above, if PRACH transmission resources arepredefined, the RA-RATI used by the primary UE for decoding may beregarded as being predefined.

The eNB may schedule a PDSCH via the PDCCH masked with the RA-RNTI andinform the UE which transmits a PRACH preamble on the specifiedresources via this PDSCH of information for scheduling uplink resourcesused to transmit an uplink signal. That is, the primary UE may detectthe PDCCH masked with the RA-RNTI, decode the PDSCH scheduled by thePDCCH and read uplink scheduling information (that is, a UL grantmessage) within the PDSCH, thereby determining resources to be used forcommunication between UEs.

The secondary UE may attempt to decode the PDCCH with the RA-RATI of theprimary UE similarly to Embodiment 7-3. Since the size of this PDCCH isequal to that of uplink grant DCI format 0 or DCI format 1A for PDSCHcompact scheduling in communication with the eNB, burden on blinddecoding is not increased from the viewpoint of the secondary UE. Thus,the secondary UE may decode the PDCCH with the RA-RATI of the primary UEand read a UL grant message for the primary UE in communication betweenUEs. Therefore, the secondary UE may check via which resources theprimary UE performs communication between UEs and appropriately performa reception operation corresponding thereto. For such an operation,since the secondary UE knows the RA-RNTI of the primary UE in advance,the eNB or the primary UE may transmit, to the secondary UE, informationfor determining the RA-RNTI of the primary UE (e.g., information aboutan index used to transmit a PRACH preamble of the UE and time/frequencyresources) in advance.

Even in this case, the primary UE must apply a power control command(that is, a power control command sent via the above-described randomaccess procedure of the specific PRACH preamble) to communicationbetween UEs without applying the power control command to communicationwith the eNB.

Embodiment 8

The present embodiment relates to a detailed method for connecting asecondary UE to an eNB.

For application of the above-described embodiments, the eNB needs toknow presence/absence of the secondary UE and the eNB needs to knowwhich secondary UE wishes to communicate with which primary UE. That is,there is a need for a method of connecting the secondary UE to the eNBin a state in which the eNB does not know presence/absence of thesecondary UE. Since the secondary UE generally has low power, thesecondary UE cannot be directly connected to the eNB and can beconnected to the eNB via the primary UE. That is, the secondary UE mayattempt to connect the primary UE and the primary UE may send connectionattempt to the eNB, thereby informing the eNB that the secondary UEattempts connection.

The secondary UE cannot be directly connected to the eNB in uplinktransmission. However, in downlink transmission, since the secondary UEperforms only a reception operation from the eNB, the secondary UE maydirectly receive a signal from the eNB. In this case, the secondary UEmay directly receive a response to a random access signal transmitted bythe secondary UE from the eNB. For example, the secondary UE may receivethe random access response via the PDCCH transmitted by the eNB.

For such an operation, the eNB may indicate PRACH resource information(PRACH preamble index, PRACH time/frequency resources, etc.) used whenthe secondary UEs are connected to the primary UE using a signal such asa broadcast message. At this time, generally, since a possibility thatthe primary UE and the secondary UE are close to each other is high, apreamble having a very short length, such as PRACH preamble format 4defined in the LTE system, may be used in order to prevent much energyfrom being consumed for transmission of the PRACH preamble.

In addition, the primary UE may periodically or aperiodically transmit aspecific signal such as SRS such that the secondary UE approaching theprimary UE perceives presence of the primary UE. The secondary UEs maybe informed of a configuration of periodic/aperiodic transmission ofsuch a specific signal via the eNB. The configuration of thetransmission of such a signal may include ID information of the primaryUE so as to enable the secondary UE to check which primary UE transmitsthe specific signal. The secondary UE which receives such informationreceives the specific signal, perceives that the primary UE is presentnear the secondary UE and attempts initial connection to the primary UE.At this time, for transmit power control between the primary UE and thesecondary UE, the intensity of the signal of the primary UE received bythe secondary UE may be reported to the primary UE or the eNB.

Alternatively, the primary UE may transmit a PRACH preamble for randomaccess and the secondary UE may detect the PRACH, thereby detecting alink between the two UEs. Since the PR ACH preamble occupies a bandwidthrelatively less than that of SRS, it is possible to detect the linkusing less frequency resources. The eNB may inform the secondary UE ofinformation about the PRACH transmitted by the primary UE via a higherlayer signal such as RRC. The eNB may instruct the primary UE totransmit the PRACH preamble using PRACH resources (e.g., PRACH resourcesreserved for handover) other than PRACH resources which may be used bythe UEs attempting initial connection. Additionally, in order to preparefor the case in which the secondary UE does not detect the primary UEsignal, the eNB may instruct the primary UE to periodically transmit aspecific PRACH preamble. The secondary UP which receives theconfiguration information of the transmission of the PRACH preambletransmitted by the primary UE from the eNB may attempt to detect thePRACH preamble of the primary LTE on IA, resources corresponding to theconfiguration information. Additionally, if the signal transmitted bythe primary UP is randomized to be specific to the primary UE, the eNBmay inform the secondary UE of information such as the ID of the primaryUE such that the secondary UE can easily detect a signal from theprimary UE.

Embodiment 9

in the above-described embodiments of the present invention, the case inwhich the secondary UP directly decodes the PDCCH from the eNB wasdescribed. At this time, when the number of PDCCH candidates decoded bythe secondary UE is too large (that is, the number of times of blinddecoding is large), complexity of the operation of the secondary UE isincreased and power consumption is also increased.

Blind decoding means an operation in which, if various PDCCH DCI formatshaving different sizes are present, a reception side does not know thesize of a DCI format of a PDCCH transmitted by a transmission side andattempts to decode candidates. In addition, blind decoding may beperformed in a common search space of UEs and/or a UE-specific searchspace.

In order to mitigate burden on blind decoding of the secondary UE, aregion in which the secondary UE performs blind decoding of the PDCCHfrom the eNB may be restricted. For example, the secondary UE may beconfigured to decode the PDCCH only in the common search space. Inparticular, if the primary UE and the secondary UE decode the samePDCCH, the secondary UE may be prevented from decoding the PDCCH in theUE-specific search space of the primary UE via such restriction. Inaddition, if transmission to the secondary UE is scheduled using arandom access procedure, since the PDCCH transmitted with the RA-RNTI istransmitted in the common search space, it is possible to avoidunnecessary operation via such restriction.

Embodiment 10

In the above-described embodiments, a method of scheduling signaltransmission/reception to/from the secondary UE at the primary UE and amethod of directly scheduling communication between UEs at the eNB weredescribed. Hereinafter, as another communication method between UEsproposed by the present invention, a method of enabling the eNB toallocate resources to be used for communication with the secondary UE tothe primary UE and then performing communication between the primary UEand one or a plurality of secondary UEs using the resources will bedescribed.

The eNB may periodically allocate specific frequency resources to theprimary UE. More specifically, the eNB may specify frequency resourceswhich may be allocated to the primary UE using higher layer signaling(e.g., RRC signaling) and indicate activation/deactivation of thespecified frequency resources via a physical layer control signal. Suchan operation may be configured similarly to the existing semi-persistentscheduling (SPS). However, since resources allocated to the primary UEby the eNB are for communication between UEs, the present invention isdifferent from the SPS scheduling method. That is, a subframe structure,a channel structure, a transmit power control method, etc. proposed bythe above-described embodiments of the present invention forcommunication between the primary UE and the secondary UE within theresources allocated to the primary UE by the eNB are applicable.

FIG. 21 is a diagram showing a wireless communication system in whichcommunication between UEs (that is, peer-to-peer communication) isperformed using dedicated resources specified by an eNB. In FIG. 21, oneof UE1, UE2 and UE3 is a primary UE to which the eNB may allocateresources in order to use specific frequency resources with a period ofseven subframes. Communication between UE1, UE2 and UE3 may be performedusing the resources.

In order to perform the operation of FIG. 21, the primary UE maytransmit, to the eNB, information about resources necessary forcommunication with the secondary UE. Such information may includelocation information of the primary and/or secondary UE, a category of aservice associated with communication between UEs (e.g., a voice serviceor a data service), the amount of necessary resources and/or duration,the number of secondary UEs, etc.

The eNB may determine resources to be allocated for communicationbetween UEs based on information reported by the primary UE.Additionally, the eNB may restrict maximum power which may be used inthe resources allocated for communication between UEs to a specificvalue and inform the primary and/or secondary UE of power restrictioninformation, in order to enable the eNB to use the resources forcommunication of another UE (communication between another UE and theeNB or communication between another UE and another UE) separated fromthe location where communication between UEs is performed even whenspecific resources are allocated for communication between UEs. Sincecommunication between UEs is generally performed between close UEs,communication may be performed with low transmit power. Thus, the eNBmay restrict power used for communication between UEs to preventinterference with another UE.

In addition, since the eNB specifies the resources to be used forcommunication between UEs, the eNB may determine/control the amount ofresources to be used for communication between UEs, quality (orinterference level), maximum transmit power, etc. in consideration ofthe kind of a service (e.g., voice or data) associated withcommunication between UEs requested by the UE or a service fee, therebycontrolling a data rate and coverage which may be used by the UE. Forexample, if the UE requests an inter-UE communication service havinghigh quality (or pays a high fee according to high service quality), theeNB may allocate resources exclusive resources) which are expected tohave a relatively low interference level, allocate a large amount ofresources or allocate a high transmit power restriction value toallocate resources for communication between UEs, thereby providing aservice having high quality, a high data rate and/or wide coverage. Incontrast, if the UE requests an inter-UE communication service havinglow quality (or pays a low fee according to low service quality), theeNB may allocate resources shared resources) which are expected to havea relatively high interference level, allocate a small amount ofresources or allocate a low transmit power restriction value to allocateresources for communication between UEs, thereby providing a servicehaving low quality, a low data rate and/or narrow coverage.

In addition, the UE may transmit, to the eNB, location information(e.g., GPS information) of the UE when requesting an inter-UEcommunication service. The eNB may allocate resources for communicationbetween UEs to the UE which requests the inter-UE communication serviceand, at the same time, allocate the same resources as the resources usedfor communication between UEs to another UE geographically separatedfrom the UE (that is, another UE which does not participate in inter-UEcommunication requested by the UE) in consideration of the location ofthe UE which requests the inter-UE communication service. Since the UEwhich participates in communication between UEs and the other UE aregeographically separated from each other, interference between the UEsmay be expected to be low even when the same resources are allocated.

Additionally, when the eNB allocates the resources for communicationbetween UEs, if the intensity of the signal of communication between theeNB and the other UE using the resources is large, resources allocatedfor communication between UEs may be subject to interference. In orderto solve such a problem, the eNB may perform a silencing operation forreducing interference in the subframe corresponding to the resourcesallocated for communication between UEs. As an example of the silencingoperation, a certain subframe may be configured as an almost blanksubframe (ABS) (a subframe in which only a common reference signal (CRS)is transmitted and the remaining resource elements are blank) or as anMBSFN subframe (a subframe in which a CRS is also not transmitted in adata region).

In addition, if resources used for communication between UEs are fixedin a frequency region, the frequency region may consistently have a hadchannel status. Accordingly, in resource allocation for communicationbetween UEs, frequency selective influence may be reduced usingfrequency hopping (a method of performing allocation while changing afrequency band).

In the resources allocated from the eNB to the primary UE forcommunication between UEs, the primary UE may establish a separate cell.FIG. 22 is a diagram showing a subframe structure when a primary UEestablishes a separate cell. In FIG. 22, the eNB allocates DL resourcesto the primary UE as resources for communication between UEs. However,the present invention is not limited thereto and the subframe structureshown in FIG. 17 or 18 is applicable when the primary UE is allocated ULresources for communication between UEs.

In the example of FIG. 22, some time-frequency resources may beallocated for communication between UEs in a subframe n. For example,first several OFDM (or SC-FDMA) symbol(s) of the subframe n becomes aregion in which a PDCCH is transmitted from the macro cell (that is, theeNB) and communication between the primary UE and the secondary UE maybe performed in the remaining OFDM (or SC-FDMA) symbol(s) of thesubframe n and the specific frequency regions 2220 and 2230. Morespecifically, the PDCCH from the primary UE to the secondary UE may betransmitted in the time-frequency region 2220 and the PDSCH from theprimary UE to the secondary UE may be transmitted in the time-frequencyregion 2230. The region 2240 other than the PDCCH transmission region2210 from the macro cell and the resource region 2220 and 2230 allocatedfor communication between UEs in the subframe n may be used to transmitthe PDSCH to the macro UE (another UE which receives a service from themacro cell). Meanwhile, a subframe n+1 indicates a general subframe towhich resources for communication between UEs is not allocated. Forexample, if the subframe n+1 is a downlink subframe, first several OFDMsymbols 2250 correspond to a PDCCH transmission region of a macro celland the remaining OFDM symbols 2260 correspond to a PDSCH transmissionregion from a macro cell to a macro UE.

As shown in FIG. 22, the primary UE may transmit a signal such as aCRS/PDCCH with a separate cell ID in the time-frequency resources 2220and 2230 allocated by the eNB to perform communication with thesecondary UE. The eNB may send, to the primary UE, information such as acell ID to be used when the primary UE establishes a cell. The secondaryUE may detect the location of the time-frequency resources in which thecell established by the primary UE appears (this information may bedirectly sent from the eNB to the secondary UE), acquire schedulinginformation from the cell established by the primary UE on thetime-frequency resources, and perform appropriate measurement(measurement for RRM, RLM, etc.).

In addition, when the primary UE transmits/receives a PDSCH/PUSCHto/from the secondary UE in the cell established by the primary UE, itis necessary to define an operation when resources less than PDSCH/PUSCHtransmission resources in a general cell are used. For example, as inthe example of FIG. 22, if the primary UE is allocated DL resources forcommunication between UEs, first several OFDM symbols 2210 of a subframein which the allocated DL resources are present are used for PDCCHtransmission of the eNB (macro cell). That is, since the primary UE musttransmit the PDSCH to the secondary UE using only the OFDM symbols lessin number than the number of OFDM symbols (2260 of FIG. 22) used forPDSCH transmission in the general cell, the PDSCH may be transmitted byapplying rate matching or puncturing. Although the primary UE transmitsthe PDSCH to the secondary UE when being allocated DL resources in FIG.22, the PUSCH may be received from the secondary UE on the resourcesallocated for communication between UEs. Even in this case, since thesecondary UE performs PDSCH transmission using SC-FDMA symbols less innumber than the number of SC-FDMA symbols used for general PUSCHtransmission, rate matching/puncturing is applicable. Meanwhile, if theprimary UE is allocated UL resources for communication between UEs,since the PDCCH of the macro cell is not present in the allocatedsubframe, all SC-FDMA symbols of the UL resources may be used. In thiscase, the primary UE may transmit the PDCCH for the secondary UE fromthe first SC-FDMA symbol of the subframe of the allocated resources.

Meanwhile, the secondary UE may access both the cell (macro cell)established by the eNB and the cell established by the primary UE andperform transmission/reception to/from the respective cells. In thiscase, the secondary UE may perform data transmission/reception similarlyto carrier aggregation. Carrier aggregation is introduced in order toaggregate a plurality of frequency bands (that is, carriers) to providea large band. One of the frequency bands corresponds to a primarycarrier (or a primary cell) and the remaining frequency bands correspondto secondary carriers (or secondary cells). If such carrier aggregationis applied, for example, a cell established by the eNB may be configuredas a primary cell (PCell) and a cell established by the primary UE maybe configured as a secondary cell (SCell). The example of the presentinvention is different from general carrier aggregation in that theSCell is present in some time/frequency regions of the PCell.

In addition, in order to reduce complexity of blind decoding of thesecondary UE, only blind decoding of one cell may be performed in onesubframe. For example, in the example of FIG. 22, in the subframe n inwhich the cell established by the primary UE (that is, SCell from theviewpoint of carrier aggregation (or from the viewpoint of the secondaryUE)) is present, only the PDCCH of the cell (that is, SCell) of theprimary UE may be searched for. In addition, in the subframe n+1 inwhich the cell (that is, SCell) of the primary UE is not present, onlythe PDCCH of the cell that is, PCell) of the eNB (from the viewpoint ofcarrier aggregation (or from the viewpoint of the secondary UE)) may besearched for. The search operation performed per PCell or SCell may beconfigured only in the UE-specific search space. That is, switching ofthe searching of the PDCCH of PCell or SCell is not applied in thecommon search space and only the PDCCH of one cell (e.g., PCell) isalways searched for in the common search space.

Embodiment 11

The present embodiment relates to a detailed method of controllingtransmit power of the primary UE in the various examples of the presentinvention.

The signal transmitted by the primary UE is classified into three types:a UL transmission signal (hereinafter, referred to as signal type 1) fortransmitting data and a control signal from the eNB to the primary UE, asignal (hereinafter, referred to as a signal type 2) for transmittingdata and a control signal from the primary UE to the secondary UE and asignal (hereinafter, referred to as a signal type 3) transmitted todetect the primary UE by dormant secondary UEs (UEs which are currentlynot connected to the primary UE but may be connected to the primary UEin the future).

Signal type 3 may be a signal such as SRS or PRACHperiodically/periodically transmitted on UL resources or a referencesignal periodically/periodically transmitted on DL resources. Here, thereference signal periodically/periodically transmitted on DL resourcesmay be a CRS based on a cell ID separately allocated to the primary UE,a UE-specific RS (DRS) specific to the secondary UE or a CRS or CSI-RSfor some antenna ports among CRSs or CSI-RSs configured by the eNB. Thesecondary UE may detect the primary UE and attempt access using signaltype 3.

Hereinafter, an example of controlling transmit power according tosignal type will be described in detail.

In case of signal type 1, as in existing communication between the eNBand the UE, the eNB may control transmit power. That is, the eNBprovides a transmit power control (TPC) command to the primary UE suchthat the primary UE may control power of the signal transmitted to theeNB. For example, the TPC command may be provided as a relative value ofprevious transmit power and the UE may accumulate the TPC command tocalculate transmit power to be applied.

Since signal type 2 is transmission from UE to UE, (as described inEmbodiment 7) transmit power of signal type 2 may not be controlledsimultaneously with transmit power of signal type 1 which transmissionform the UE to the eNB but transmit power of signal type 2 may becontrolled separately from transmit power of signal type 1. For example,the eNB may directly provide a transmit power control command to theprimary UE to control transmit power of signal type 2 transmitted fromthe primary UE to the secondary UE or the eNB may set a maximum value oftransmit power of the primary UE and the primary UE may control transmitpower of signal type 2 in consideration of the status of the radio linkbetween the primary UE and the secondary UE within the maximum value.

Since the main purpose of signal type 3 is to determine the distancebetween a certain secondary UE and a certain primary UE, in powercontrol of signal type 3, it is important to accurately measure pathloss between the primary UE and the secondary UE rather than powerreceived by the secondary UE. Here, although the secondary LE reportsthe received signal intensity of signal type 3 to the eNB, the eNB mustknow transmit power of the signal (that is, power transmitted by theprimary UE) in order to estimate path loss. Accordingly, there is a needfor a transmit power control method of enabling the eNB to know thepower used to transmit signal type 3 at the primary UE.

For example, the eNB may instruct the primary UE to fix the transmitpower value of signal type 3 to a predetermined value using a higherlayer signal (e.g., an RRC signal). In this case, since eNB knows thatthe primary UE always transmits signal type 3 with the predeterminedfixed power value, since the received signal power value of signal type3 is received from the secondary UE, path loss between the primary UEand the secondary UE may be calculated.

As another example, while the eNB controls transmit power of signal type3 transmitted by the primary UE, the eNB may directly inform the primaryUE of the transmit power value of signal type 3 whenever the primary UEtransmits signal type 3. That is, the power control command from the eNBmay not represent a relative value of previous transmit power but mayrepresent an absolute value of transmit power to be applied to currenttransmission. In this case, if the UE misses a power control command inthe method of accumulating the power control command provided as arelative value to derive a current transmit power value, it is possibleto prevent generation of a difference between transmit power indicatedby the eNB and transmit power applied by the UE.

As another example, the primary UE may report the transmit power valueof currently applied signal type 3 to the eNB. The transmit power valuemay be reported periodically or when a specific event occurs (that is,in an event-triggered manner). The specific event may occur, forexample, when receive power of a signal from a neighboring cell is equalto or greater than a predetermined threshold or when transmit power ofsignal type 3 is changed to a value having a predetermined differencewith previous transmit power or may aperiodically occur when the eNBrequests to report the transmit power value.

The above-described embodiments of the present invention are applicableto communication between UEs in a licensed hand. The principle of thepresent invention is applicable to communication between a UE and an eNBin an unlicensed band. For example, assume that an LTE based systemoperates using a cognitive ratio method in an unlicensed band. Forexample, in a band in which communication between the eNB and the UE isnot allowed and another wireless system is preferentially allowed in anLTE system, a method of determining whether communication of anotherwireless communication system which is preferentially allowed is presentand performing LTE-based communication only when an incumbent user isnot present may be considered. In this case, it is necessary to sensewhether another wireless system is used in every subframe. In this case,as described in the examples of the present invention, carrier sensingmay be performed in first several OFDM (or SC-FDMA) symbol intervals ofa subframe and transmission from the eNB to the UE in an LTE system maybe performed in the remaining region of the subframe. In addition, theexamples of a subframe structure, a channel structure and transmit powercontrol when UL resources or DL resources described in the examples ofthe present invention are allocated for communication between UEs areapplicable to communication between an eNB and a UE in an unlicensedband. Thus, it is possible to mitigate/eliminate interference ofcommunication between an eNB and a UE with communication of anothersystem and avoid/eliminate interference from communication of anothersystem.

FIG. 23 is a flowchart of a method for communication between UEsaccording to an embodiment of the present invention.

In step S2310, an eNB may allocate resources for communication betweenUEs (communication between a first UE and a second UE) and transmitscheduling information including power control information to the firstUE and/or the second UE along with such resource allocation information.

In step S2320, the first UE may schedule communication between the firstUE and the second UE using resources allocated by the eNB forcommunication between UEs and inform the second UE of such schedulinginformation. The first slot of the subframe among resources forcommunication between UEs may include a control signal for communicationbetween UEs and the second slot may include a data signal between theUEs.

In step S2320, the first and second UE may perform communication betweenUEs based on scheduling information of step S2320.

In FIG. 23, the first UE may correspond to a primary UE and the secondUE may correspond to a secondary UE.

In the method for communication between UEs according to an example ofthe present invention described with reference to FIG. 23, details ofthe above described various embodiments of the present invention may beindependently applied or 2 or more embodiments may be applied at thesame time. In this case, overlapping details will be omitted for thedescription for simplicity and clarity. The method for communicationbetween UEs according to an example of the present invention describedwith reference to FIG. 23 is applicable to communication between an eNBand a UE for reducing interference with another system or another cell.In this case, the operation of the first UE may be regarded as theoperation of the eNB and the operation of the second UE may be regardedas the operation of the UE communicating with the eNB.

FIG. 24 is a diagram showing the configuration of atransmission/reception device according to the present invention.

The transmission/reception device 2400 of FIG. 24 may be a userequipment device, for example. The user equipment device 2400 accordingto the present invention may include a reception module 2410, atransmission module 2420, a processor 2430, a memory 2440, and aplurality of antennas 2430. The plurality of antennas 2450 indicatesthat the user equipment device supports MIMO transmission and reception.The reception module 2410 may receive various signals, data, andinformation on a downlink from the base station. The transmission module2420 may transmit various signals, data, and information on an uplink tothe base station. The processor 2430 may control the overall operationsof the user equipment device 2400.

The user equipment device 2400 according to the embodiment of thepresent invention may be configured to perform inter-UE communicationwith another UE device. The processor 2430 of the user equipment device2400 may be configured to receive scheduling information includinginformation for allocating resources for communication between UEs fromthe eNB. The processor 2430 may be configured to perform communicationwith the other UE via one or more of the transmission module 2410 or thereception module 2420 based on the scheduling information. The firstslot of the subframe among resources for communication between UEs mayinclude a control signal for communication between the UEs and thesecond slot of the subframe may include a data signal between the UEs.

Moreover, the processor 2430 of the user equipment device 2400 performsa calculation/operation process on information received by the useequipment device 2400, information that is to be transmitted outside,and so on. The memory 2440 may store the processed information for apredetermined period of time, and the memory 2440 may be replaced byanother element, such as a buffer (not shown).

In the above-described detailed configuration of the base station deviceand the user equipment device, details of the above-described variousembodiments of the present invention may be independently applied or 2or more embodiments may be applied at the same time. In this case,overlapping details will be omitted from the description for simplicityand clarity.

Furthermore, the above description of the present invention may also beequally applied to a relay station device functioning as a downlinktransmission subject or an uplink reception subject. The description ofthe user equipment device may also be equally applied to a relay stationdevice functioning as an uplink transmission subject or a downlinkreception subject.

The above-described embodiments of the present invention can beimplemented by a variety of means, for example, hardware, firmware,software, or a combination of them.

In the case of implementing the present invention by hardware, thepresent invention can be implemented with application specificintegrated circuits (ASICs), Digital signal processors (DSPs), digitalsignal processing devices (DSPDs), programmable logic devices (PLDs), isprogrammable gate arrays (FPGAs), a processor, a controller, amicrocontroller, a microprocessor, etc.

If operations or functions of the present invention are implemented byfirmware or software, the present invention can be implemented in theform of a variety of formats, for example, modules, procedures,functions, etc. The software codes may be stored in a memory unit sothat it can be driven by a processor. The memory unit is located insideor outside of the processor, so that it can communicate with theaforementioned processor via a variety of well-known parts.

The detailed description of the exemplary embodiments of the presentinvention has been given to enable those skilled in the art to implementand practice the invention. Although the invention has been describedwith reference to the exemplary embodiments, those skilled in the artwill appreciate that various modifications and variations can be made inthe present invention without departing from the spirit or scope of theinvention described in the appended claims. For example, those skilledin the art may use each construction described in the above embodimentsin combination with each other. Accordingly the invention should not belimited to the specific embodiments described herein, but should beaccorded the broadest scope consistent with the principles and novelfeatures disclosed herein.

Those skilled in the art will appreciate that the present invention maybe carried out in other specific ways than those set forth hereinwithout departing from the spirit and essential characteristics of thepresent invention. The above exemplary embodiments are therefore to beconstrued in all aspects as illustrative and not restrictive. The scopeof the invention should be determined by the appended claims and theirlegal equivalents, not by the above description, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. Also, it will be obvious to thoseskilled in the art that claims that are not explicitly cited in theappended claims may be presented in combination as an exemplaryembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

INDUSTRIAL APPLICABILITY

The embodiments of the present invention are applicable to variousmobile communication systems.

The invention claimed is:
 1. A method of performing communicationbetween a first UE (User Equipment) and a second UE in a wirelesscommunication system, the method performed by the first UE andcomprising: being configured, by a higher layer, to use a firstidentifier which is different from a second identifier for acommunication between the first UE and the base station to receive, froma base station, downlink control information comprising schedulinginformation for a communication between the first UE and the second UE;receiving, from the base station, the downlink control information;decoding the downlink control information using the first identifier;and performing the communication between the first UE and the second UEbased on the scheduling information.
 2. The method according to claim 1,wherein the downlink control information includes a Cyclic RedundancyCheck (CRC) scrambled by the first identifier.
 3. The method accordingto claim 1, wherein the scheduling information includes resourceinformation used for the communication between the first UE and thesecond UE.
 4. The method according to claim 1, wherein the schedulinginformation includes a Transmission Power Control (TPC) command for thecommunication between the first UE and the second UE.
 5. The methodaccording to claim 1, wherein the communication between the first UE andthe second UE is performed in a subframe which does not overlap in timewith an uplink transmission from the first UE to the base station.
 6. Afirst User Equipment (UE) performing a communication with a second UE ina wireless communication system, the first UE comprising: a transmitter;a receiver; and a processor that controls the first UE, wherein thefirst UE is configured, by a higher layer, to use a first identifierwhich is different from a second identifier for a communication betweenthe first UE and the base station to receive, downlink controlinformation comprising scheduling information for a communicationbetween the first UE and the second UE, and wherein the processorreceives, from the base station, the downlink control information,decodes the downlink control information using the first identifier, andperforms the communication between the first UE and the second UE basedon the scheduling information.
 7. The method according to claim 6,wherein the downlink control information includes a Cyclic RedundancyCheck (CRC) scrambled by the first identifier.
 8. The method accordingto claim 6, wherein the scheduling information includes resourceinformation used for the communication between the first UE and thesecond UE.
 9. The method according to claim 6, wherein the schedulinginformation includes a Transmission Power Control (TPC) command for thecommunication between the first UE and the second UE.
 10. The methodaccording to claim 6, wherein the communication between the first UE andthe second UE is performed in a subframe which does not overlap in timewith an uplink transmission from the first UE to the base station.